HKSAR v. CHEUNG KIE CHUNG

CACC 213/2020

[2024] HKCA 1149

IN THE HIGH COURT OF THE

HONG KONG SPECIAL ADMINISTRATIVE REGION

COURT OF APPEAL

CRIMINAL APPEAL NO 213 OF 2020

(ON APPEAL FROM HCCC NO 292 OF 2019)

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REASONS FOR JUDGMENT

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Hon Zervos JA (giving the Reasons for Judgment of the Court):

1.  This application concerned the defence of diminished responsibility where the uncontradicted psychiatric evidence was that the applicant was suffering from an abnormality of mind at the time of the killing, and raised for consideration (1) the relevance of psychological evidence on the question of whether the abnormality of mind substantially impaired his mental responsibility for the act that caused the victim’s death; (2) whether the uncontradicted psychiatric evidence warranted the withdrawal of the charge of murder from the jury; and (3) the appropriate direction on the meaning of the word “substantially”.

2.  The applicant was charged with the murder of his wife, Chan Wai Man (“Madam Chan”), contrary to common law and punishable under section 2 of the Offences against the Person Ordinance (Cap 212).[1] At his arraignment, the applicant pleaded not guilty to murder but pleaded guilty to manslaughter by provocation or diminished responsibility, which was rejected by the prosecution. On 26 November 2020, after being tried before A Pang J (as she then was) (“the Judge”) and a jury, the applicant was convicted by a majority verdict of 5 to 2. He was sentenced to life imprisonment as required by law.

3.  The applicant applied for leave to appeal against his conviction.

4.  The applicant was represented by Mr Graham Harris, SC, and Mr Lee Shu Wan, at the trial and the appeal. The respondent was represented by Mr Ira Lui and Ms Lilly Wong in the appeal but not at trial. On 4 January 2024, we adjourned the leave application because Mr Harris was unwell, but unfortunately, he was unable to attend the adjourned hearing due to his illness. We nevertheless had the benefit of his written submissions, which comprehensively dealt with the arguments in support of the applicant’s challenge to his conviction. In this judgment, we refer to Mr Harris as having argued the grounds of appeal based on the written submissions, although Mr Lee had also helpfully addressed us in oral submissions.

5.  On 2 February 2024, having heard the arguments of the parties, we quashed the applicant’s conviction and ordered that he be retried on a fresh indictment. We said we would hand down our reasons in due course. These are the reasons for our decision.

6.  We should note that we have also considered the recent judgment of the Court of Final Appeal in HKSAR v Tsim Sum Kit, Ada [2]. The Court, in that case, upheld the imposition of a legal burden on a defendant to prove the defence of diminished responsibility on a charge of murder. The Court stated that it is only where the reverse burden provision requires the defendant to prove an essential ingredient of the offence with which he is charged, relieving the prosecution of the burden of proving that ingredient beyond a reasonable doubt, that the presumption of innocence is engaged.[3] The Court explained that “proof of a relevant abnormality of mind is not an ingredient of the offence of murder. The burden placed on a defendant to establish the defence of diminished responsibility only arises when the prosecution has satisfied the burden of proving beyond reasonable doubt that the defendant is otherwise guilty of murder.”[4]

The prosecution case

7.  Most of the evidence at trial in the present case was not disputed and was adduced by way of admitted facts.

8.  The applicant was an Associate Professor of the Faculty of Engineering at the University of Hong Kong (“HKU”). He was married to Madam Chan, with whom he had two children, Nancy Cheung (“Nancy”) and Scot Cheung (“Scot”). At the material time, the four of them lived in Room 1601 on the 16^th floor of Wei Lun Hall, a residential hall of HKU (“Room 1601”). Also staying in Room 1601 were Madam Chan’s sister, Chan Wai Yin, Tracy, (PW1) (“Tracy”), and Tracy’s daughter, who were visiting Hong Kong. They slept on the sofa in the living room. The applicant had his office nearby in Room 7-5 on the 7^th floor of the Haking Wong Building at HKU (“Room 7-5”).

9.  On or about 17 August 2018, the applicant killed Madam Chan in their bedroom in Room 1601.

10.  After killing his wife, the applicant, on the afternoon of 18 August 2018, purchased 8 matte white wooden boards from a timber shop on Des Voeux Road West, Sai Wan.[5] The wooden boards were later used to construct a box in which he placed his wife’s body.

11.  On 20 August 2018, the applicant and Nancy made a missing person report in respect of Madam Chan at the Western Police Station. On 21 August 2018, in response to the report, police officers went to Room 1601 for investigation.[6]

12.  At about 10:40 am on 22 August 2018, the applicant ordered a “GoGoVan”, a hire van, which he used to transport his wife’s body in the wooden box. At around 11:00 am, the applicant was captured on CCTV footage pushing a wooden box from the car park of Wei Lun Hall to the GoGoVan, which was driven to a drop-off area near the Haking Wong Building. He then pushed the wooden box into a lift of that building, and upon reaching the 7^th floor, he moved the box out of the lift.[7]

13.  On the morning of 23 August 2018, the applicant purchased 6 more matte white wooden boards from the timber shop in Sai Wan.

14.  On 24 August 2018, police officers went to the applicant’s office in the Haking Wong Building to make enquiries with the applicant.[8]

15.  On the afternoon of 28 August 2018, police officers returned to the applicant’s office for further investigation. The applicant was present, and they searched his office. They found under a table the wooden box, which was made of wooden boards fixed with screws, edges treated with white sealant and the inside laminated with white Formica. In the wooden box was a suitcase containing Madam Chan’s body. Around her neck was a length of electric wire twisted with the left shoulder strap of her bra. The applicant was arrested for the offence of murder.[9]

16.  A forensic pathologist concluded that Madam Chan died from “pressure on the neck”. An expert in forensic science explained how the loose ends of the wires around Madam Chan’s neck were tucked into a knot, which could have been formed by using a pair of pliers (because of the presence of indented marks on the plastic sheath of the wires) or with bare hands.[10] There was no question that the applicant constructed the wooden box containing Madam Chan’s body, as his fingerprints were found on various parts of it.[11]

17.  The prosecution case was that the applicant murdered Madam Chan in cold blood for financial reasons.

18.  There were several unusual financial dealings between Madam Chan and the applicant. It was admitted that a $6.7 million cheque payable to Madam Chan dated 25 June 2018 was drawn on the applicant’s bank account (Exhibit D3).[12] This cheque had not been deposited, but would not have been honoured because there were insufficient funds in the bank account. It was also admitted that on 16 August 2018, a $4 million cheque payable to Madam Chan dated the same day (Exhibit D2) was drawn from the applicant’s bank account and deposited into a Citibank account, which had been opened by Madam Chan that day. The cheque was dishonoured as there were insufficient funds in the bank account.[13]

19.  On the morning of 16 August 2018, Madam Chan and her sister, Tracy, went to a branch of the DBS Bank to inquire about the opening of a bank account. Mr Chiu (PW2), the branch manager of the DBS Bank, told Madam Chan that she could get a reward by using one more name to open an account. Madam Chan followed this up by telephoning the applicant, insisting he see Mr Chiu. She told Mr Chiu to visit the applicant, which he did. Mr Chiu went to HKU and met the applicant who appeared “very calm and very normal” during the meeting.[14] The meeting did not last very long because the applicant was busy and had to send Mr Chiu away.

20.  In the afternoon, Madam Chan and Tracy went to a branch of Citibank, where Mr Lee (PW3) assisted Madam Chan in opening an account, in which she deposited a $4 million cheque. She then left, but was seen wandering outside the bank. A short while later, Madam Chan returned to the bank and asked Mr Lee to explain the new account to the applicant over the telephone. Mr Lee said he could not recall if he told the applicant about Madam Chan depositing a cheque into the account.[15]

The defence case

21.  The applicant gave evidence and also called his daughter, Nancy, to give evidence on his behalf. The defence case was that he killed Madam Chan because he had been provoked or was suffering from diminished responsibility, and that it had nothing to do with any financial dispute between them.

22.  The applicant testified that he met Madam Chan in 1986 while studying for a university degree in the United Kingdom. They got married in 1987, and Madam Chan gave birth to Nancy. In the early 1990s, the family of three moved back to Hong Kong. In 1992, the applicant became an Associate Professor at the Faculty of Engineering at HKU. In addition to teaching at HKU, the applicant was appointed the warden of Wei Lun Hall in 2007. As part of his employment package, he was entitled to accommodation, and he and his family lived in Room 1601. Madam Chan was a housewife except between 1994 and 1996. The applicant described Madam Chan as opinionated, insistent and moody. He said he would accommodate Madam Chan whenever he could, but the children, on the other hand, would often quarrel with their mother.

23.  Nancy testified that her father was a very easy-going person, who did the bulk of the housework. In contrast, her mother was extroverted, impulsive and stubborn: she would scold people and throw a tantrum if she did not get her way. Even when her parents had heated arguments, her father would not rebuke her mother. He would usually walk away, muttering to himself. She said her mother could be “sharp-tongued” when scolding others. She noticed that her father had become less patient and more easily irritated since 2013, and arguments between her parents had been more frequent since 2016. She heard her mother criticize her father by saying, “If it were not for me, you would be sleeping on the streets, and you would be a beggar.” Her mother sometimes would say similar hurtful things, even in front of relatives.[16]

The applicant’s financial situation

24.  Over the years, the applicant and Madam Chan purchased five properties in their joint names, which they leased. The applicant’s salary income allowed the couple to take out mortgages to finance the purchases. They repaid the mortgages with the rental incomes.

25.  They were not forthcoming with each other about their financial situation except for their joint transactions. Separately, Madam Chan bought and sold stocks from time to time and she was proud of her success as an investor. The applicant denied that Madam Chan intended to buy another property in August 2018 because they would have had to pay double stamp duty, and the mortgages taken out for the other properties had not yet been fully repaid. Furthermore, he and Madam Chan would not be able to pass the bank’s stress test for mortgage finance.[17]

26.  During cross-examination of the applicant, it was revealed that the rental incomes from four properties could not cover the mortgage repayments and related expenses. In 2011, the applicant took out a credit card loan of $500,000 from the DBS Bank, which he was still repaying in August 2018 in monthly instalments at the minimum amount required. In December 2016, the applicant borrowed about $764,000 from the Bank of East Asia (“BEA”) by way of an overdraft facility. By 16 August 2018, he still owed BEA the sum of $710,000. Also, in 2016, the applicant took out a loan of $400,000 from Hang Seng Bank, with a repayment schedule of 5 years. As of 16 August 2018, the credit balance of the applicant’s bank accounts in his sole name was about $120,000. The applicant acknowledged that he was highly geared and that all his properties were still mortgaged.[18]

27.  On the morning of 31 May 2018, Madam Chan told the applicant that he owed her $6.7 million and demanded that he write a post-dated cheque in her favour as proof of his debt. At the time, the applicant did not have his cheque book with him, so he wrote an “IOU” (exhibit P7[19]), which effectively stated that he owed Madam Chan $6.7 million and if payment was not made on the same day he stood to be penalised by paying an additional $1 million. The applicant went to his office immediately to retrieve his cheque book in order to write Madam Chan a cheque in the sum of $6.7 million, which was dated 25 June 2018 (exhibit D3[20]). He had no idea why the cheque had to be post-dated and did not ask Madam Chan because he wanted to avoid being scolded by her.[21]

28.  Previously, in February 2018, Madam Chan had raised the same issue, and the applicant had written her a cheque for $6 million. The applicant’s combined cash flow with different banks amounted to only $500,000 (with an overdraft facility of $700,000). Hence, if any attempt was made to deposit a cheque of more than that amount, the cheque would be dishonoured. The applicant said Madam Chan knew this, although he did not expressly tell her not to bank the cheque.[22]

The applicant’s physical and emotional health

29.  In April 2018, the applicant suffered from a bacterial infection and was admitted to Queen Mary Hospital for two weeks. He had lost about 17 pounds of weight over the period from 2008 to 2018, and from around the end of 2017, he felt very tired.[23] He never told his family or anyone about feeling depressed, his loss of interest and his deteriorating memory. However, his colleagues noticed a change in him as he was unable to finish his markings.[24]

30.  The applicant had a heavy workload because of his commitments to teaching and wardenship, particularly after 2012. He also took up preparing expert reports. Madam Chan sometimes complained that he had too many jobs and was not getting promoted. There were occasions when the couple had heated arguments, Madam Chan would say hurtful things to him, such as “you are useless”, “if I have to rely on you, I would be turning into a beggar”, “eat faeces”, “drop dead”, and “pok gai”. She would say these things in front of their children, and the applicant felt humiliated. Prior to the offence, no matter how upset he was because of the arguments, he was never violent with Madam Chan, nor was she violent with him.[25]

31.  There were times when the applicant lost his temper. In 2014, when the applicant was discussing an issue with his colleague on the telephone at home, Madam Chan told him not to get involved. The applicant got angry, pulled the telephone and its charger from the wall and threw them out of the window. There was another occasion when someone had detached wires on the floor for an upcoming robot competition, having told his staff not to touch the wires. The applicant scolded the staff member very badly and subsequently apologised to that person. There were other occasions when he lost control. The applicant explained that towards August 2018, he became easily irritated and would mutter to himself.[26] In cross-examination, he acknowledged that in the period leading up to August 2018, he would get angry easily and would talk back to Madam Chan.[27]

The events leading up to the killing

32.  There was a dispute between the applicant and Madam Chan about a toilet seat in one of their flats, which featured predominantly in this case. In 2014, after they had purchased their fifth property, they repainted the washroom from green to white. The toilet seat was green, so Madam Chan told the applicant to swap it with Scot’s toilet seat, which was white. Scot was unhappy about the swap. The property was leased, and in 2017, after the tenancy was terminated, the applicant removed the white paint from the wall, and the washroom was green again. Madam Chan instructed the applicant to swap the toilet seat with Scot’s seat so that the colour of the wall and the seat matched. Scot was angry that his toilet seat had been exchanged again with someone else’s seat. He taped it shut and smeared chocolate spread all over the toilet seat used by his mother and Nancy. Nancy felt this was all her mother’s fault and told her to clean it up. However, Madam Chan did not think she was responsible, so she did nothing about it.[28]

33.  Late in the evening of 15 August 2018, Madam Chan told the applicant to write her a cheque for $4 million, and he did so without asking questions because he did not want to upset her. As previously, he expected her not to honour the cheque since she only wanted the cheques as proof of his debts. The applicant confirmed that two persons from different banks talked to him on 16 August 2018 about opening a new bank account, but as the applicant was busy at the time, he did not pay attention to what they were saying. Madam Chan did not talk about depositing a cheque for $4 million into her new account with DBS, nor did Mr Lee of Citibank, mention that Madam Chan made such a deposit when he telephoned him. The applicant only learned after the killing that Madam Chan had deposited the $4 million cheque into a Citibank account.[29]

34.  On 16 August 2018, the applicant was busy with student interviews in Wei Lun Hall. Despite the applicant telling Madam Chan on the telephone that he would be engaged the whole day, Madam Chan sent someone from the DBS bank to see him at the university during lunchtime. Madam Chan did not talk about depositing the $4 million cheque into the new account. The applicant politely dealt with the DBS agent and continued with the interviews in the afternoon. He then met Madam Chan for dinner at HKU, and they returned to Room 1601 around 9:00 pm. Tracy and her daughter were in Room 1601. At that stage, the applicant was not stressed or upset in any way. When Nancy got home at around 10:00 pm, she was in a bad mood and demanded Madam Chan to clean up the toilet, which was still taped shut and dirty with chocolate spread. Madam Chan refused and closed the door of her bedroom. Nancy threw a clothes rack at the door, got into Madam Chan’s room, dragged her mother out and demanded that she clean the toilet. Nancy testified that the applicant witnessed the argument, and became irritated and muttered to himself. The applicant did not intervene and left Room 1601 for a meeting he had arranged with the students of Wei Lun Hall.[30]

35.  When the applicant returned to Room 1601 at about 11:50 pm, Tracy told him that Nancy had packed some things and left. The applicant was angry that his wife had caused his daughter to leave home at such a late hour, but he said nothing. He got ready for bed, while Madam Chan was sitting on the edge of the bed watching a drama on the computer. At about 12:30 am, Madam Chan requested the applicant to get some orange juice from the kitchen, which he did. Madam Chan took a sip of the orange juice and sent a message to Nancy, demanding she return the juice and get a refund. Upon seeing this, the applicant got very angry. Nancy had bought the orange juice as they had run out of it, and Madam Chan was unreasonable in telling her off at such an hour. He rebuked his wife for scolding their daughter in such a manner, saying that she would never come home again. In reply, Madam Chan blamed the applicant for not stopping Nancy from assaulting her. The couple also argued about the mess with the toilet.

36.  Madam Chan said to him, “If you are so smart you do everything about the home. I don’t care anymore. I am leaving.” The applicant retorted, “Just leave”, taking off his glasses and laying down on the bed, with his back to his wife.[31] After a while, Madam Chan said, “You wish after everything had been fixed it should be you who leaves. Without me how could you have so many flats?” The applicant said, “Please be fair. We are only able to take out a loan because I can use my salary as a proof for repayment.” Madam Chan answered, “Is it very smart to have a job? Without me how could you buy the flats? Relying on you I would be a beggar.”[32]

37.  Madam Chan told the applicant to leave and she used her right leg to kick him out of the bed. He fell to the floor. He intended to go to the living room, so he felt under the bed to retrieve his slippers. Instead, he felt some wire. The applicant thought, “You had so much to say”. He grabbed the wire and climbed on the bed. Madam Chan had her back to him but apparently, she felt his presence and said, “I told you to leave. What are you going to do coming and mounting back on the bed?” The applicant was furious and said in his mind, “How come you still have so much to say?” He wrapped the wire around Madam Chan’s neck. He did not know what happened next.[33]

38.  When the applicant realized what had happened, Madam Chan’s upper body was slumped forward. He tried to undo the knot in the wire around Madam Chan’s neck but was unsuccessful. He realized he had killed his wife. The only thought he had was to prevent others from seeing the body. He got a blue suitcase outside Scot’s room, placed Madam Chan’s body in it and put the suitcase back where it had been.[34]

The applicant’s conduct after the killing

39.  On the morning of 17 August 2018, the applicant told Tracy that Madam Chan had gone out, and then drove Scot to work. Tracy and her daughter left for Disneyland. He later returned to Room 1601, and took the blue suitcase outside Scot’s room to the outside of the living room, where there was a green suitcase. The applicant took Madam Chan’s body out of the blue suitcase and put it in the green suitcase. He placed the green suitcase on the balcony and put the blue suitcase back outside Scot’s room. The applicant had no plan and took one step at a time. In the afternoon, he attended the admission interviews of Wei Lun Hall, followed by a meeting with his secondary classmates in the evening.[35]

40.  On the afternoon of 18 August 2018, the applicant went to a timber shop in Sai Wan and purchased eight wooden boards, intending to make a box to conceal Madam Chan’s body, which would start to smell due to the summer heat. He made a box at home, placed the green suitcase in it and put the box on the balcony of Room 1601, where it stayed for three days.[36]

41.  On 19 August 2018, the applicant sent a WhatsApp message to Madam Chan’s telephone to say, “How are you?”, which the applicant admitted to be “a camouflage”. He went swimming in the afternoon and walked his dog in the evening. He told Tracy that Madam Chan might have gone on a trip to the Mainland.[37]

42.  On 20 August 2018, the applicant went with Nancy to the Western Police Station to make a missing person’s report. He knew the report was false. He told the police that Madam Chan might have left home possibly for a trip. By then, he had moved the wooden box from the balcony to the lift lobby outside Room 1601 and covered it with miscellaneous objects. When the police came to Wei Lun Hall for investigation, the applicant falsely told them that Madam Chan was seen leaving the building on the CCTV with the intent to mislead them (in fact, it was an unknown female). In the afternoon, the applicant disposed of Madam Chan’s passport and a pair of her shoes to give the false impression that she was away on a trip.[38]

43.  On 21 August 2018, the police came to Room 1601 for further investigation. On 22 August 2018, the applicant hired a GoGoVan in order to move the wooden box from outside Room 1601 to his office in the Haking Wong Building. He did so because of the police investigation on the previous day and feared the box would soon be discovered. In fact, when he was pushing the box in the car park of Wei Lun Hall, he unexpectedly encountered police officers and lied to them about what was contained in the box. On the morning of 23 August 2018, the applicant returned to the timber shop for more boards to make another box. He then dismantled the new box and placed the boards in the Haking Wong Building so that if he was asked by the police, he could claim he had dismantled the box. During these days, he did not tell anyone about the killing. He felt terrible when Tracy and his children kept asking about Madam Chan and pretended to join them in locating his wife. He knew people would know very soon. On 28 August 2018, the police went to the applicant’s office and discovered Madam Chan’s body.[39]

44.  On a day between 23 and 26 August 2018, Tracy told Nancy that there were a number of missed calls and messages on Madam Chan’s telephone. In particular, Tracy told Nancy that a bank staff member said Madam Chan had deposited a $4 million cheque, which was dishonoured. Nancy then asked the applicant about the matter. The applicant replied that he knew about the dishonoured cheque. He told her that he had intended to transfer money to the current account for the cheque, but because he and Madam Chan had had an argument in the early hours on 17 August 2018, he had not done the transfer out of spite.[40]

45.  The applicant was a person of clear record and had no previous encounters with the law.

The expert evidence

46.  The defence called three doctors to testify as experts in respect of the applicant’s partial defences of provocation and diminished responsibility.

47.  Dr Bonnie Siu (DW7) was a consultant psychiatrist at Siu Lam Psychiatric Centre. She had prepared a report at the request of the police, for which she had interviewed the applicant on seven occasions between September and October 2020.[41] She made a psychiatric diagnosis that the applicant had been suffering from moderate to severe depression around the time of the killing.

48.  Dr Siu observed that the applicant had a depressed and anxious mood with increased irritability, loss of interest and enjoyment, increased fatigability, reduced attention and deterioration in memory. She admitted her diagnosis might be limited by the fact that she interviewed the applicant two years after the killing. She was of the opinion that the applicant was not malingering.

49.  Of diminished responsibility, Dr Siu found the applicant had prominent symptoms of depression, which could have impaired his ability to form a rational judgement. She was of the view that the impairment from the applicant’s depression was “substantial”, in that it was “more than minimal”. The fact that the applicant had gone to great lengths to cover up the killing did not affect her assessment of specific aspects of his depression. She said that agitation, one of the symptoms of depression, could have impaired the applicant’s ability to exercise self-control.[42] She pointed out that the symptoms of the applicant’s depression would impair, to a certain extent, his mental responsibility, with the qualification that it was ultimately for the jury to decide on this question.[43] In cross-examination, she said that the applicant had not told her about the cheques Madam Chan had demanded and his financial situation. She said it would be outside her expertise to comment on the applicant’s mental responsibility if motive were taken into consideration, which might affect the degree of impairment.[44]

50.  Dr Robyn Ho (DW8) was a psychiatrist in private practice. She had prepared a report at the defence’s request, and for that purpose, she had interviewed the applicant on two occasions between April and May 2020.[45] She came to the conclusion that the applicant had been suffering from major depressive disorder at the time of the offence, which impaired his mental responsibility. She explained that when a sufferer of major depressive disorder became very irritated or angry, it could cause him to lose self-control.[46] As for the applicant’s efforts to conceal the killing, she was of the opinion that such acts were inconsistent with the applicant’s general character as he told her he only had done what the circumstances demanded without planning.[47] In cross-examination, Dr Ho admitted she could not know whether the applicant had difficulty in controlling himself but that it was “very possible” that he was not able to make rational judgements at the time of the offence. She also stated that the applicant did not tell her about the cheques Madam Chan had demanded from him.[48] In re-examination, Dr Ho said that knowing about the cheques would not change her diagnosis of the applicant.[49]

51.  Dr Sammy Cheng (DW9), a clinical psychologist in private practice, had prepared a report and had interviewed the applicant on two occasions.[50] He found that the applicant had a serious issue with emotional control, and under little or minor stress, the applicant would have “huge” and “abnormal” emotional reactions. He was of the view that it was caused by the applicant’s workload and deteriorating health. He found the applicant a victim of chronic, moderate to serious psychological abuse at home because of Madam Chan’s verbal violence. He said the applicant was especially susceptible to losing control more than an ordinary person.[51] In cross-examination, Dr Cheng said that the applicant told him that he did not know why he killed his wife, and that he might have had problems controlling his emotions at the time but did not know why. He confirmed that the applicant did not tell him about the cheques Madam Chan had made him issue.[52] In re-examination, Dr Cheng considered that the matter with the cheques was irrelevant to the issue of self-control.[53]

The grounds of appeal

52.  The grounds of appeal settled by Mr Harris and Mr Lee, for the applicant, were as follows:

Ground 1: The Judge should have withdrawn the charge of murder from the jury, or alternatively she failed to adequately sum up the prosecution’s basis for inviting the jury to reject the unequivocal views of the defence psychiatrists.

Ground 2: The Judge misdirected the jury on the meaning of “substantial” in the context of “substantial impairment” for diminished responsibility.

Ground 3: The Judge wrongly withdrew the defence psychologist’s evidence from the jury on the issue of diminished responsibility.

Grounds 1 and 2: Uncontradicted expert medical evidence and the issue of substantial impairment

53.  We will deal with Grounds 1 and 2 together as they involve a consideration of the same authorities concerning expert medical evidence and the element of substantial impairment in respect of the defence of diminished responsibility.

54.  By Ground 1, Mr Harris submitted that the Judge failed to withdraw the charge of murder from the jury, or alternatively, she did not sum up the prosecution’s basis for inviting the jury to reject the unequivocal view of the psychiatric experts as stipulated in R v Brennan[54].

55.  Whilst prosecuting counsel cross-examined the applicant to the effect that he did not suffer from depression at the time of the killing[55] and that the diagnosis of the experts was unreliable, he conceded in his closing speech that the finding by the psychiatrists that the applicant was suffering from depression was not disputed.[56] This meant that the issue between the parties was the extent of the impact of the depression on the applicant’s mental responsibility for the killing.[57] The prosecution submitted that mental responsibility was not substantially impaired by his depression despite not having adduced any expert evidence to counter that called by the defence. By contrast, the defence impressed upon the jury that for them to reject the evidence of the two psychiatrists, they “would have to have a really good reason”, particularly because the expert evidence was unchallenged.[58]

56.  The Judge summed up the prosecution’s case[59] and provided a written hand-out direction on diminished responsibility, which contained this paragraph:[60]

“17. You are entitled to take into consideration all the material before you, including the evidence relating to and surrounding the killing, the circumstances under which it occurred, the acts and the statements of the Accused and his manner at, before and after the time of the killing, and so in the end, it is for you to say, in the light of all the evidence, not only the medical evidence, whether it was more likely than not that the Accused was suffering from an abnormality of mind at the time of the killing which substantially impaired his mental responsibility.”

57.  Mr Harris took issue with the Judge’s above remarks because the psychiatrists were in agreement that the applicant’s ability to control himself and to judge his conduct and behaviour before and after the killing was consistent with his suffering from depression. It was argued that the Judge was wrong to point generally to the surrounding circumstances of the killing as capable of providing a proper basis on which the jury could reject the defence. Moreover, the Judge did not identify any specific evidence that could provide a proper basis for the rejection of the defence and, therefore, her directions were insufficient and amounted to an error of law. He relied on the general proposition by the Court of Appeal in Brennan that where the prosecution contested a defence of diminished responsibility but did not adduce expert evidence, the other facts and circumstances relied on by the prosecution to undermine the defence should be specifically identified by the judge to the jury.

58.  Mr Harris further submitted that because the evidence relied on by the prosecution was not capable of rebutting the defence since both psychiatrists stated that the applicant’s conduct before and after the killing was consistent with his suffering from depression – this was a case where the murder charge should have been withdrawn from the jury. As the Judge did not take this approach, it was therefore incumbent on her in her summing-up to identify the evidential basis on which the jury would be entitled to reject the otherwise uncontradicted expert evidence in accordance with Brennan. He complained that despite a strong request from the defence that directions along the lines of R v Golds [61] and Brennan be given, the Judge refused to adopt such an approach.[62]

59.  In Ground 2, Mr Harris took issue with the following directions by the Judge on substantial impairment:[63]

“… If there was impairment of responsibility, you must consider whether it was a substantial impairment. There is no scientific test which can give you the answer to the question whether the impairment was substantial. Substantial is an ordinary English word which imports a question of degree and to which you will bring your own experience in deciding whether the impairment was substantial in this case without substituting a different word for it.

(12), In the course of her evidence, Dr Siu referred to the impairment of the accused being more than minimal. I should tell you that in the context of diminished responsibility, it is not the law that any impairment beyond the trivial will suffice. It must be such as is judged by you to be substantial.

(13), You must approach the question in a broad common sense way. You must ask yourselves, having heard what the medical experts have said and looking at all the evidence, including what the accused did, do we, looking at it broadly as people of ordinary common sense, think it more likely than not that there was a substantial impairment or diminishing or weakening of his mental responsibility, which includes the ability to exercise willpower, to control what he did?”

60.  Mr Harris referred to Golds, noting that the Supreme Court held that ordinarily a jury need not be directed on the meaning of “substantial”, and should normally be given to understand that the expression is an ordinary English word, which imports a question of degree, and that whether in the case before it the impairment can properly be described as substantial is for the jury to resolve. If it has been introduced to the jury that there is a spectrum from merely trivial to total impairment, between which a substantial impairment sits, that it will be for the judge to determine whether it is necessary to further direct the jury that it is not enough that the impairment be merely more than trivial, it must be judged by the jury to be substantial.[64] He stated that this approach had been approved by the Court of Appeal in HKSAR v Jutting[65].

61.  Mr Harris complained that the way the Judge explained substantial impairment to the jury gave the impression that more than minimal impairment, as stated by Dr Siu, would not qualify in law as being substantial. He submitted that the Judge should have made it clear that, while not every more than minimal impairment will be substantial, it was open to the jury to determine this “more than minimal” impairment was substantial. This became particularly important when the jury sought further guidance on this issue by the question it raised during its deliberations.[66] It was argued that the response by the Judge was inadequate, being no more than a repetition of what she had previously told the jury and that she declined to remind the jury of Dr Ho’s evidence.[67]

The respondent’s submission

62.  Mr Lui submitted that Brennan was not the last word from the English courts on the issue of uncontested medical evidence on diminished responsibility, and subsequent cases had significantly qualified and moved away from the approach in Brennan.

63.  A number of cases relevant to the present issue were R v Khan (Dawood) [68], Golds, R v Blackman [69], R v Hussain [70] and R v Sargeant [71]. Mr Lui submitted that the Supreme Court in Golds only endorsed part of the judgment in Brennan, that is, the long-standing principle that there must be some rational evidential basis for challenging agreed expert evidence, but whether an accused’s mental responsibility was diminished was a question for the jury.[72] In emphasising the primacy of the jury in determining the issue, the Supreme Court held that a trial judge must exercise great caution before accepting the defence of diminished responsibility and removing the case from the jury. The fact that psychiatric evidence was unchallenged by itself was not a justification for doing so.[73] Applying Golds, subsequent decisions of the English Court of Appeal reverted to the broad approach in Khan (Dawood)[74], which was decided before Brennan[75]. As such, Mr Lui submitted that notwithstanding the uncontradicted medical evidence, a murder charge should not be withdrawn if there are serious factual issues to be tried by the jury. He noted that whilst Golds [76] offered some suggestions on jury directions in respect of diminished responsibility, the Court of Appeal in Sargeant [77] stated that this did not require specific legal directions to be given in every case involving the defence.

64.  It was cogently argued by Mr Lui that there was a rational and legitimate basis for the prosecution to challenge the defence of diminished responsibility, despite the prosecution not adducing expert medical evidence in response to the defence expert medical evidence. He submitted that although the psychiatric evidence was not contradicted, it was nevertheless qualified and not unequivocal in relation to the element of substantial impairment.

65.  Dr Siu’s diagnosis was limited by the fact of the assessment was conducted over two years after the killing and hence involved retrospective deductions, and the truthfulness of the information supplied by the interviewees.[78] Dr Siu also defined “substantial” to mean “more than minimal” which was a lesser threshold as held in Golds.[79] Furthermore, Dr Siu qualified her opinion on substantial impairment because of the time that had passed between her interviews with the applicant and the killing, and that it was based on the interviewee telling her the truth. She accepted that a monetary dispute with the deceased could affect the substantiality of the degree of the impairment, and that if motive was to be considered, it would be beyond her expertise as a psychiatrist.[80]

66.  Dr Ho stated that the applicant was suffering from major depressive disorder that would be “likely substantially to have impaired his mental responsibility”. However, she stated that it was “possible” that the applicant “could have lost of control” and “very possible that he was not able to make rational judgement”, although she could not say that had actually happened. She explained that she believed the applicant would have experienced difficulty in forming rational judgement because he was suffering from a major depressive disorder but could not tell to what extent.[81]

67.  Mr Lui submitted that given the equivocal and guarded evidence of the experts on substantial impairment, there was no valid basis to withdraw the charge of murder from the jury.

68.  Mr Lui further argued that the jury were entitled to assess the quality and weight of the medical evidence, even if it were uncontradicted.[82] There were material factual issues regarding the existence of a monetary dispute between the applicant and the deceased and the applicant’s conduct in carrying out and covering up the killing. These factual issues could only be resolved by the jury. He noted that Dr Siu accepted that a monetary dispute might affect the substantiality of the degree of impairment, although the question of a motive was outside her expertise.[83] Even though Dr Ho did not consider the monetary dispute material to the applicant’s likely mental state, it still remained a relevant factual issue for the jury to resolve. Mr Lui referred to the case of Sargeant [84], as an instance where the Court of Appeal accepted that a monetary dispute between the parties was a rational basis for rejecting the defence case of diminished responsibility.

69.  As for the complaint regarding the inadequacy of the summing-up, Mr Lui submitted that the defence expert medical evidence on the element of substantial impairment was equivocal as seen by the qualifications of the expert opinions and other related factual issues, such as the monetary dispute and the applicant’s conduct before and after the killing. He pointed out, correctly in our view, that these were matters which the Judge canvassed extensively in her summing-up.

70.  The Judge provided the jury with a detailed explanation of the expression “abnormality of mind” and that it was not in dispute that the applicant was suffering from a depressive episode of moderate to severe severity or major depressive disorder.[85] She stressed the relevance of the medical evidence when considering the issue of substantial impairment, but emphasised that the issue of substantial impairment was a matter for them to resolve.[86] She added:[87]

“You are entitled to take into consideration all the material before you, including the evidence relating to and surrounding the killing, the circumstances under which it occurred, the acts and the statements of the accused and his manner at, before and after the time of the killing. And so in the end, it is for you to say, in the light of all the evidence not only the medical evidence, whether it was more likely than not that the accused was suffering from an abnormality of mind at the time of the killing which substantially impaired his mental responsibility.”

71.  After an extensive review of the psychiatric evidence, the Judge, in her customary thorough manner, drew the jury’s attention again to the following matters:[88]

“(1), In this case before you, there is no contradictory medical evidence coming from the prosecution to counter Dr Siu and Dr Ho’s evidence. The prosecution did not call any psychiatrist and therefore there is no contradictory medical evidence coming from the prosecution to counter Dr Siu and Dr Ho’s evidence. So you would agree that if you were to reject the evidence of Dr Ho and Dr Siu, there should be a proper basis for doing so. And the proper basis would be as what I have set out in the handout.

(2), You have heard from both Dr Siu and Dr Ho that the accused post killing conduct or the extent of such conduct was no surprise to both of them and was consistent with a person suffering from substantial impairment. Of course, in relation to their opinion on substantial impairment, I have just revisited with you what each psychiatrist said. But given that their evidence is uncontradicted, you may agree that you should not simply based on the accused post-killing conduct and the extent of such conduct to rule out the likelihood that the impairment was substantial.

(3), The prosecution in this case suggests a motive. Dr Siu frankly admitted that motive was outside her expertise as a psychiatrist. Of course, Dr Ho when I revisited her evidence with you, she said as to the matters concerning the cheques she said those would not make any difference to her opinion.

(4), As both Dr Siu and Dr Ho indicated, the question of substantial impairment is ultimately a question for you. This is trial by jury, not trial by experts. So approach the question in a broad common sense way by taking into account all the circumstances and all the evidence, not just the medical evidence, although you would no doubt agree that it is important evidence, in answering the question of whether the impairment was substantial or not.”

72.  Immediately after these remarks, the Judge again reminded the jury of the salient features of the expert medical evidence. At the conclusion of the evidence, there was no dispute that the applicant was suffering from depression and, therefore, the issue for the jury was whether his mental condition substantially impaired his mental responsibility for the killing of his wife. The issue of substantial impairment was the focal point of the trial, and a significant dividing line between the prosecution and the defence. This issue was made abundantly clear by the parties and the Judge in her summing-up to the jury. In our view, this was a case where the defence expert evidence was tentative or qualified on the element of substantial impairment, in respect of which there were also related factual issues for the jury to resolve. There was a rational basis on which the jury could decline to accept the defence expert evidence on this element of the defence of diminished responsibility.[89]

73.  Mr Lui argued that the law on substantial impairment was well settled: it must be “more than merely trivial”, and it must be “substantial”.[90] In the present case, Dr Siu said the impairment was “more than minimal”[91], whereas Dr Ho could not tell the extent of the applicant’s mental impairment or his difficulty in making rational judgements.[92] As the defence did not re-examine the psychiatrists on the issue, Mr Lui contended that it was not open for them to suggest the experts could have meant that the impairment was considerably “more than minimal”. He also said that at no time during the numerous trial discussions did the defence ask the Judge for the direction now advocated by the applicant.[93]

74.  Mr Lui pointed out that the direction sought by the applicant was not suggested by Golds[94]. In R v David Squelch [95], which applied Golds, it was held that where the evidence goes no further than showing that the accused suffered some “partial impairment”, the Judge is not obliged to direct the jury that as a matter of law, a partial impairment may be capable of supporting diminished responsibility.[96]

75.  In the respondent’s submission, it was argued that the Judge’s directions on diminished responsibility amply and clearly conveyed to the jury the key issues: (1) the word “substantially” is an ordinary English word and it imports a question of degree[97]; (2) it is for the jury to assess whether the impairment can properly be described as “substantial”[98]; (3) whilst the impairment must pass the “merely trivial” threshold, it is not the law that any impairment beyond trivial will suffice[99]; and (4) the issue must be assessed in a broad common sense way[100].

76.  As for the adequacy of the Judge’s further direction in response to the jury’s question, Mr Lui said that the Judge was right not to refer to Dr Ho’s evidence because it did not pertain to the jury’s question. The jury sought clarification on the issue of substantial impairment because of Dr Siu’s evidence that “substantial” meant “more than minimal” and the Judge’s directions on this element. The Judge discussed her answer with counsel, which she duly gave to the jury without any dissension from the parties. The jury acknowledged that they were satisfied with the answer and did not ask for any further assistance on the meaning of “substantial impairment”.[101]

77.  We say immediately that we find no substance in the applicant’s complaint concerning the Judge’s answer to the jury’s question. She discussed the question with counsel and they agreed on how it should be answered. The Judge gave a perfectly proper answer to the question emphasising her previous directions to them.

Discussion

78.  In examining the English authorities on diminished responsibility referred to by the parties, it is necessary to understand the changes made in that jurisdiction to the original statutory provision that enacted this defence. In Hong Kong, the defence of diminished responsibility remains rooted in the terms of the original statutory provision. It should be noted that the English decisions were addressing the amendment of section 2 of the Homicide Act 1957 by section 52 of Coroners and Justice Act 2009. Such an amendment has not been made to section 3 of the Homicide Ordinance (which is identical to section 2 of the Homicide Act before the amendment). Section 3(1) reads as follows:

“Where a person kills or is a party to the killing of another, he shall not be convicted of murder if he was suffering from such abnormality of mind (whether arising from a condition of arrested or retarded development of mind or any inherent causes or induced by disease or injury) as substantially impaired his mental responsibility for his acts and omissions in doing or being a party to the killing.”

79.  The amendment of section 2 of the Homicide Act 1957 made significant changes to the defence of diminished responsibility.[102] As amended, the section is in these terms:

“(I) A person (‘D’) who kills or is a party to the killing of another is not to be convicted of murder if D was suffering from an abnormality of mental functioning which— (a) arose from a recognised medical condition, (b) substantially impaired D's ability to do one or more of the things mentioned in subsection (IA), and (c) provides an explanation for D’s acts and omissions in doing or being a party to the killing.

(IA) Those things are— (a) to understand the nature of D’s conduct; (b) to form a rational judgement; (c) to exercise self-control.

(IB) For the purposes of subsection (I)(c), an abnormality of mental functioning provides an explanation for D’s conduct if it causes or is a significant contributory factor in causing D to carry out that conduct.”

80.  The Supreme Court in Golds stated that the effect of the new statutory formulation of diminished responsibility required the jury to decide (i) whether the accused suffered from an abnormality of mental functioning; (ii) whether the abnormality arose from a recognised medical condition; (iii) whether the abnormality substantially impaired his ability (a) to understand the nature of his conduct; or (b) to form a rational judgement; or (c) to exercise self-control; and (iv) whether the abnormality caused or significantly contributed to his killing the deceased.[103]

81.  For the defence to succeed, it required that the accused’s ability to understand his own conduct, make rational judgements or exercise self-control was “substantially impaired” by a recognised medical condition. The learned authors of Smith, Hogan, and Ormerod’s Criminal Law described the practical effects of the changes as narrowing the scope of defence and creating the opportunity for experts to have even greater influence over the outcome. However, they acknowledged, citing Golds, that jurors remain at liberty to disregard the expert evidence left to them.[104] Under the law as it stands in Hong Kong, what has to be substantially impaired is the defendant’s mental responsibility for acting as he did. In contrast, under the new law in the United Kingdom, what has to be shown to be substantially impaired is the defendant’s ability to do any of the things mentioned in section 2(1A), namely “(a) to understand the nature of his conduct; (b) to form a rational judgement; (c) to exercise self-control.”

82.  The previous defence of diminished responsibility in section 2 of the Homicide Act 1957 (the same as section 3(1) of the Homicide Ordinance) has been the subject of criticism by legal academics because the defence was defined broadly and imprecisely to apply where the accused’s “abnormality of mind” substantially impaired his “mental responsibility”. The requirement of a “substantially impaired mental responsibility” has been replaced with an element that makes no reference to “responsibility”. Instead, it must be shown that the abnormality, arising from a recognised medical condition, substantially impaired the accused’s ability to understand the nature of his conduct; or form a rational judgement; or exercise self-control. The stark contrast between the two provisions, is illustrated by the emphasis in the original provision of “abnormality of mind”, and “abnormality of mental functioning” in the new provision.

83.  It was succinctly explained in Brennan that the new provisions are “to ensure a greater equilibrium between the law and medical science” and “most, if not all, of the aspects of the new provisions relate entirely to psychiatric matters.”[105] To this end, it is said that the new provisions have “medicalised” the defence of diminished responsibility.[106]

The issue of substantial impairment

84.  Regardless of the changes to the defence of diminished responsibility, subsequent English case law is still relevant in this jurisdiction in certain aspects, particularly cases which address the concept of “substantial impairment”. However, care needs to be taken when considering the English decisions and the commentaries, in light of the changed elements of the defence under the new law in the United Kingdom.

85.  It is appropriate that we set out a general overview of the law of the defence of diminished responsibility in Hong Kong. The partial defence to murder of diminished responsibility, if proven, reduces liability to manslaughter, thereby avoiding the mandatory life sentence. It is based on the general principle that a person’s responsibility for committing a serious offence should be assessed in light of any substantial mental impairment which that person suffered at the time. The central feature of the defence is the existence of an abnormality of mind which can be shown to have substantially impaired the accused’s mental responsibility at the time of the killing.

86.  The prosecution must prove that the accused caused the death of the deceased, and that he or she had the requisite mental state for murder at the time of the killing. If that is proven, the accused bears the burden of establishing, on the balance of probabilities, the defence of diminished responsibility. There are three elements to the defence. First, at the time of the killing, the accused was suffering from an abnormality of the mind. Secondly, the abnormality of the mind arose from one of the following causes: from a condition of arrested or retarded development of the mind, or from any inherent cause, or induced by disease or injury. Thirdly, the abnormality of mind substantially impaired the accused’s mental responsibility for the killing.

87.  The third element requires the jury to determine whether the accused’s capacity for rational conduct was impaired, whether that impairment was substantial, and whether there was the necessary causal relationship between the impairment and the act which the accused committed. The term “substantial” has been interpreted to mean “more than trivial”. However, the Supreme Court in Golds [107] has held that this interpretation is not correct, and that juries should not generally require an explanation of the meaning of “substantial” since it is an ordinary English word.[108] If, however, they do need an explanation, “the judge should explain that whilst the impairment must indeed pass the merely trivial before it need be considered, it is not the law that any impairment beyond the trivial will suffice”.[109] This has been said to impose a stricter test.[110] As the accused bears the burden of proving the defence, it is generally considered that the requirement of substantial impairment means that the impairment must be more than trivial or minimal. Expert evidence may be admitted on the question of whether a person’s mental responsibility was substantially impaired, but ultimately, it is a matter for the jury to determine, after a consideration of all the evidence. This reflects the role juries play in considering issues of moral responsibility as representatives of the community, notwithstanding they are required to deal with medical concepts, particularly in circumstances where psychiatrists frequently comment on all aspects of the defence of diminished responsibility. As identified in Brennan, it is often both “legitimate and helpful” for a psychiatrist to express a view on whether there was substantial impairment.[111]

88.  Lord Hughes JSC, in his judgment in Golds, with whom the other judges agreed, said that the meaning of “substantially” was to be understood not in the sense of “present rather than illusory or fanciful, thus having some substance” but in the sense of “important or weighty” as in “a substantial meal” or “a substantial salary” or “significant and appreciable”.[112] He explained that when the word “substantially” is used in conjunction with “impairment” for the reduction of murder to the lesser offence of manslaughter “there is a weighty reason for it and not merely a reason which just passes the trivial.”[113] He considered that if the occasion for elucidation of “substantially” does arise, “the judge’s first task is to convey to the jury, by whatever form of words suits the case before it, that the statute uses the ordinary English word and that they must avoid substituting a different one for it.”[114] He acknowledged that various phrases had been used that were acceptable ways of elucidating the sense of the statutory requirement.[115] However, he counselled against substituting the statutory language, noting that, “[t]he jury must understand that ‘substantially’ involves a matter of degree, and that it is for it to use the collective good sense of its members to say whether the condition in the case it is trying reached that level or not.”[116]

89.  Lord Hughes provided the following guidance when addressing the partial defence of diminished responsibility:[117]

“(1) Ordinarily in a murder trial where diminished responsibility is in issue the judge need not direct the jury beyond the terms of the statute, and should not attempt to define the meaning of ‘substantially’. Experience has shown that the issue of its correct interpretation is unlikely to arise in many cases. The jury should normally be given to understand that the expression was an ordinary English word, that imports a question of degree, and that whether in the case before it the impairment can properly be described as substantial was for the jury to resolve.

(2) If, however, the jury had been introduced to the question of whether any impairment beyond the merely trivial would suffice, or if it had been introduced to the concept of a spectrum between the greater than trivial and the total, the judge should explain that, whilst the impairment had to pass the merely trivial before it needed to be considered, it was not the law that any impairment beyond the trivial would suffice. The judge should likewise make that clear if a risk arose that the jury might misunderstand the import of the expression; whether this risk arises or not is a judgment to be arrived at by the trial judge who is charged with overseeing the dynamics of the trial. … Illustrative expressions of the sense of the word may be employed so long as the jury is given clearly to understand that no single synonym was to be substituted for the statutory word.”

90.  The Court of Appeal in David Squelch, in applying Golds, held that it was not the case that a detailed direction as to the meaning of the word “substantially” was required and approved the following direction to the jury that:[118]

“‘Substantially’ is an ordinary English word on which you will reach a conclusion in this case, based upon your own experience of ordinary life. It means less than total and more than trivial. Where, you, the jury, draw the line is a matter for your collective judgment.”

91.  It would appear that this direction, using the phrase “more than trivial”, set a lower threshold test than that advocated in Golds might be applied when the circumstances warranted it.[119]

92.  The Supreme Court’s judgment in Golds has been the subject of criticism, which has been encapsulated by Mr Karl Laird in his commentary to the case report in the Criminal Law Review.[120] He noted that the Supreme Court concluded that, ordinarily, judges should not define the meaning of “substantially” for the jury, but if the trial judge feels that a risk has arisen that the jury has misunderstood the import of the expression “substantial”, he will have to direct the jury that a more than merely trivial impairment is insufficient to make out the defence. He made two points. First, the Supreme Court expressed concern about the possibility that different juries may attribute different meanings to “substantially”, but by its judgment the possibility of inconsistent interpretations of the term still remains. Secondly, in order to achieve consistency in application and parity between defendants, the Supreme Court should have held that the direction must be given in every case, particularly when the Supreme Court held that the inclusion of the term “substantially” fulfills an important function by ensuring that defendants are not found guilty of manslaughter rather than murder in the absence of sufficiently weighty reasons.

93.  Mr Laird also criticised the Supreme Court for the meaning it attributed to the term “substantially”. He argued that Golds went much further than any of the cases that have considered the issue in the past which require the defendant to demonstrate a high degree of impairment.

94.  The debate about the need for an explanation of the meaning of the word “substantial” has a common theme with why the courts have avoided explaining the standard of proof required in a criminal trial that the jury be “sure”: R v Yeung Kuen Chi [121]. The concern is that in the process of seeking to explain a plain and simple word, which is capable of understanding without explanation, the result may be to obscure or limit its meaning. Lord Hughes, in Golds, emphasised that there are many examples of ordinary English words incorporating questions of degree, which are left to juries to apply without attempts at further definition. He listed numerous examples, including the word “sure”, noting that in “all these cases the understandable itch of the lawyer to redefine needs to be resisted. Any attempt to find synonyms for such ordinary English expressions, although they involve questions of degree, simply complicates the jury’s exercise, and leads to further semantic debate about the boundaries of meaning of the synonym.”[122]

95.  We consider that the trial judge, in normal circumstances, should give guidance to the jury on the word “substantially” by setting its parameters, that is, it is not minimal or trivial and not total, and emphasising it is an ordinary English word, to which the jury bring their everyday experiences and common sense when determining whether the impairment is substantial in the circumstances before it. This will ensure, at least to this extent, that there is a common understanding between the medical experts and the judges of fact as to the meaning of “substantially”.

96.  The suggested direction on the element of “substantial impairment” in Specimen Direction, Chapter 106, Diminished Responsibility, 2020 Revision, is as follows:

“3. that the abnormality of mind, arising from one or more of those causes, substantially impaired the defendant’s mental responsibility for his acts which caused V’s death:

The expression ‘mental responsibility for his acts’ involves consideration of the extent to which his mind was answerable for his physical acts. That includes consideration of the extent of his ability to exercise willpower to control those acts.

If there was impairment of responsibility, you must consider whether it was a substantial impairment. There is no scientific test which can give you the answer to the question whether the impairment was substantial. It is an ordinary English word to which you will bring your own experience. It does not mean total, nor does it mean trivial or minimal. You must approach the question in a broad, common sense way. You must ask yourselves, having heard what the medical witnesses have said and looking at all the evidence, including what the defendant did: ‘Do we, looking at it broadly as people of ordinary common sense, think it more likely than not that there was a substantial impairment or diminishing or weakening of his mental responsibility, [an expression] which includes the ability to exercise willpower to control what he did?’ [123]

If the answer to that question is ‘Yes’, then you must acquit the defendant of murder and find him guilty of manslaughter.

If you think there might have been some impairment but you find that it was not substantial - in other words, that it was something which did not really make much difference to his mental responsibility, even though it may have made it harder to control himself - then your answer would be ‘No’ and your verdict would be guilty of murder.”

97.  In our view, the specimen direction provides suitable guidance and explanation to a jury on the third element of diminished responsibility, particularly in respect of the phrase “substantially impaired”.

98.  In the present case, the Judge, in her directions to the jury, addressed the issue of substantial impairment as follows. She said there was no scientific test that could give the jury at the answer to the question of whether the impairment was substantial. She explained that, “‘Substantial’ is an ordinary English word which imports a question of degree to which you will bring your own experience in deciding whether the impairment was substantial in this case without substituting a different word for it.” She then mentioned that Dr Siu in her evidence referred to the impairment of the accused being more than minimal. She told them that “it is not the law that any impairment beyond the trivial will suffice, it must be such as is judged by you to be substantial.” She added that they must approach the question “in a broad, common sense way” and consider all the evidence.[124] On this element of the defence of diminished responsibility, the Judge applied the terms of the specimen direction.

99.  We are satisfied that in all the circumstances the Judge gave an adequate direction on the meaning of “substantially”, and it was apparent that the jury had a clear understanding of the word after the Judge had answered the question they asked.

The uncontradicted expert medical evidence

100.  Mr Harris argued that the Judge ought to have withdrawn the charge of murder from the jury because there was no evidence providing a proper and rational basis for rebutting the defence of diminished responsibility. He relied on Brennan [125], in which the Court of Appeal held that in the absence of expert evidence adduced by the prosecution to contradict the defence expert evidence on any rational and proper basis, the judge should withdraw the murder charge from the jury. The Court observed that where the prosecution proposes to contest a defence of diminished responsibility, they should generally adduce expert evidence and/or identify other facts and circumstances under which the jury is invited to reject such a defence.[126] If the prosecution does not adduce expert evidence, the judge should identify the facts and circumstances and remind the jury that there must be a “rational and proper basis” before they can reject uncontradicted expert evidence.[127]

101.  In addressing the complaint under this ground, it is appropriate to note the remarks of Davies LJ, giving the judgment of the Court, in Brennan. He considered that in that case, the charge of murder should not have been put to the jury where the partial defence of diminished responsibility was unequivocally supported by reputable expert evidence, which was not contradicted by any prosecution expert evidence. He emphasised that “in criminal trials cases are decided by juries, not by experts”, but “juries must base their conclusions on the evidence”.[128] He then addressed the circumstances where the expert evidence was not in dispute, stating, “Where there simply is no rational or proper basis for departing from uncontradicted and unchallenged expert evidence, then juries may not do so.”[129] (Emphasis added). There may be circumstances where the defence expert evidence is uncontradicted by prosecution expert evidence but nevertheless challenged for legitimate and valid reasons. The Supreme Court in Golds, in its obiter remarks, affirmed part of the judgment in Brennan that there must be some “rational evidential basis” for challenging the medical evidence, which was a jury question, and a murder charge ought not be withdrawn “simply on the basis that the medical evidence points one way”.[130] The extent to which the Supreme Court affirmed the statements in Brennan regarding the question of uncontradicted expert evidence was encapsulated by the Court Martial Appeal Court in Blackman by the following remarks:

“43. It is important to note the emphasis in the Golds judgment not only on the prosecution’s right (if not duty) to assess the medical evidence and to challenge it, where there is a rational basis for doing so, but also on the primacy of the jury in determining the issue. It is clear that a judge should exercise caution before accepting the defence of diminished responsibility and removing the case from the jury (see paragraph 50). The fact that the prosecution calls no evidence to contradict a psychiatrist called by the defence is not in itself sufficient justification for doing so. In the light of the judgment in Golds, we see no reason not to follow the broad approach of this court in R v Khan (Dawood) [2009] EWCA Crim 1569, [2010] 1 Cr App R 4, to which reference was made in Brennan, which we would express as follows: it will be a rare case where a judge will exercise the power to withdraw a charge of murder from the jury when the prosecution do not accept that the evidence gives rise to the defence of diminished responsibility.”

102.  As observed in Brennan [131] and approved in Golds [132], if there are other facts or circumstances that might cast a different light on otherwise uncontradicted defence expert medical evidence on diminished responsibility, and the matter is to be left to the jury, one would expect them to be highlighted by prosecuting counsel in discussion with the judge prior to closing speeches, and in due course specifically identified to the jury by the judge in the summing-up.

103.  Mr Harris contended that there was no evidence to contradict the defence of diminished responsibility. It was submitted that there was only evidence of the general circumstances surrounding the offence, which the experts agreed was consistent with their view of the applicant’s depression and the impairment it caused him. It was argued that the failure to withdraw the charge of murder invited the jury to substitute personal opinions as to the significance of the applicant’s conduct before and after the killing for the expert evidence without the benefit of any cross-examination of the experts on those points.

104.  Mr Harris argued that even if the Judge was entitled to leave the murder charge to the jury, she failed adequately to direct the jury on the evidence capable of forming a proper basis on which the jury could reject the defence. It was specifically complained that the Judge failed to point out that the prosecution had not put such a case to the expert witnesses. In the circumstances, her directions did not satisfy the requirement in Brennan.

105.  In reference to Dr Siu’s evidence as to the meaning of substantial, the prosecution put to the jury that it was not that any impairment beyond trivial would suffice and that they had to consider the whole of the evidence and circumstances.[133] The prosecution submitted that the applicant’s actions at each stage were rational; that he had the ability to control himself and judge his conduct;[134] and that his depression did not substantially impair his mental responsibility for the killing.[135] The applicant argued that the only evidence of his ability to control himself and to judge his conduct was from the psychiatrists and the psychologist, all of whom agreed those abilities were impaired at the relevant times. Whilst there was such evidence (although qualified), there was also evidence of the applicant’s account to them and his testimony in court as to what he said and did before, during and after the killing. The jury, in considering the whole of the evidence, were entitled to consider the applicant’s account of what he said and did at the relevant times and put such weight on these matters as they thought appropriate. The prosecution relied on the applicant’s post-killing conduct to dispel the defence submission that his cognitive abilities were impaired to the extent that he could not appreciate the wrongfulness of his conduct.

106.  It was plain to the jury, as reflected in the summing-up, that there was no contradictory medical evidence from the prosecution, and that the applicant was suffering from depression. As emphasised with the jury, the issue for them was whether the applicant’s state of depression substantially impaired his mental responsibility for killing his wife.

107.  Mr Harris relied on the decision in Brennan to argue that the murder charge in the circumstances of this case should have been withdrawn. The Court in Brennan, citing R v Khan (Dawood) [136], agreed that where the defence of diminished responsibility was raised by the defence but contested by the prosecution, the judge had the power to withdraw a charge of murder from the jury at the close of evidence. The Court noted that this was a reflection of the Galbraith principles, which are “an application of the fundamental principle that juries may only properly convict on evidence capable of justifying a conviction and a qualification of any asserted general principle that all criminal trials must be left to be decided by a verdict of the jury.” [137] This statement by the Court should be considered in the context of the Court of Appeal’s decision in Re Secretary for Justice’s Reference (Nos 1-3/2021) [138], where the principles stated in R v Galbraith [139] and Attorney General v Li Fook Shiu Ronald [140] were reaffirmed.

108.  The Court in Brennan [141], agreed with the scenario postulated by Professor Ormerod in his review of the amended provisions of section 2 that it was possible to argue that the charge of murder ought to be withdrawn from the jury only where the medical evidence supporting the defence of diminished responsibility is uncontradicted and there is no other evidence rebutting diminished responsibility. However, the Court explained that the withdrawal was not confined solely to such a scenario and that there may be cases where the “other evidence” is too tenuous or, taken at its highest, insufficient to permit a rational rejection of the defence of diminished responsibility.

109.  After referring to the position stated in Khan (Dawood)’s case, the Court in Brennan, went on to say:

“67. … We add, however, that in the light of the new provisions of section 2 as amended, with its significantly different structure and affect, pursued by the Crown of the charge of murder in the face of a defence of diminished responsibility which is unequivocally supported by reputable expert evidence but which is not contradicted by any prosecution expert evidence should, we venture to suggest, become relatively uncommon. There may, of course, be cases where the defence expert evidence is tentative or qualified. Possibly too there may be cases where substantial inroads can be made into the defence expert psychiatric evidence by cross-examination, even in the absence of expert evidence adduced by the Crown. Otherwise, if there is reason to think that the opinion of the defence psychiatric expert(s) supporting a defence of diminished responsibility is or may be wrong in its conclusion or wrongly premised or inadequately reasoned or inadequately related to the facts or otherwise suspect then it is surely not unreasonable (at all events in most of such cases) to expect the Crown to adduce its own expert evidence in order properly to make such points for the jury’s evaluation. Accordingly, where the Crown proposes to contest a defence of diminished responsibility the new provisions set out in section 2, as amended, should be taken as an encouragement for the Crown to adduce its own expert evidence to support its stance.

68. We also add that if any particular case there are other facts or circumstances which might cast a different light on otherwise uncontradicted defence expert medical evidence on diminished responsibility and the matter is to be left to the jury, one would expect those facts and circumstances to be highlighted by prosecuting counsel in discussion with the judge prior to closing speeches and in due course specifically identified to the jury by the judge in the summing up: as capable of providing a rational basis on which the jury could decline to accept the expert evidence called by the defence if that evidence has not otherwise been contradicted or doubted by any expert evidence called by the Crown.”

110.  On this issue, the Supreme Court in Golds considered the decision of Brennan. It was noted that there may be cases where the prosecution has accepted that the correct verdict is guilty of manslaughter on the grounds of diminished responsibility, and there is no need for a trial. It was observed that in Brennan because of the psychiatric testimony and on the state of the evidence, the prosecution could not properly ask the jury to convict of murder unless it was to reject one or more parts of the expert evidence, emphasising that the jury was not bound by the expert. The Supreme Court went on to explain:[142]

“49. … In some cases, pre-planning especially involving meticulous preparations, may indicate self-control which gives grounds for rejecting an opinion that self-control was substantially impaired. In others, there may be legitimate grounds for asking the jury to disagree about the level of impairment. In yet further cases, it may be perfectly proper to ask the jury to conclude that it was the drink or drugs which led to the killing, whilst the underlying medical condition was in the background. That is not by any means an exhaustive catalogue of questions which a jury may properly be invited to decide. However, as the Court of Appeal rightly held, if the jury is to be invited to reject the expert opinion, some rational basis for doing so must at least be suggested, and none had been a trial nor was on appeal. …”

111.  The Supreme Court[143] further observed that whilst it may be agreed that the ordinary principles of R v Galbraith are capable of being applied in a trial where the sole issue is diminished responsibility, a court ought to be cautious about doing so, and for several reasons. The first was that a murder trial was a particularly sensitive event, and if the issue was diminished responsibility, a killing with murderous intent must, ex hypothesi, have been carried out. The second was that the onus of proof in relation to diminished responsibility was on the defendant and that the Galbraith process was generally a conclusion that no jury, properly directed, could be satisfied that the prosecution had proved the relevant offence so that it was sure. Accordingly, in the context of diminished responsibility, murder could only be withdrawn from the jury if the judge was satisfied that no jury could fail to find that the defendant had proved it. The third was that a finding of diminished responsibility was not a single issue matter and required the defendant to prove the elements of the defence. It was noted that whilst the effect of the changes in the law had emphasised the importance of medical evidence, the questions concerning substantial impairment and causation were essentially a jury question.

112.  In its concluding remarks on this issue, the Supreme Court stated:

“51. Where, however, in a diminished responsibility trial the medical evidence supports the plea and is uncontradicted, the judge needs to ensure that the Crown explains the basis on which it is inviting the jury to reject that evidence. He needs to ensure that the basis advanced is one which the jury can properly adopt. If the facts of the case give rise to it, he needs to warn the jury that brutal killings may be the product of disordered minds and that planning, whilst it may be relevant to self-control, may be consistent with disordered thinking. While he needs to make it clear to the jury that, if there is a proper basis for rejecting the expert evidence, they may do so because the decision is theirs and not that of the expert, it will also ordinarily be wise to advise the jury against attempting to make themselves amateur psychiatrists, and that if there is undisputed expert evidence the jury will probably wish to accept it, unless there is some identified reason for not doing so. To this extent, the approach of the court in Brennan is to be endorsed.”

113.  It needs to be appreciated that the statements referred to in the English cases were made in the context of the amended provisions of section 2, where the changes to the defence of diminished responsibility gave significantly more scope to the importance of expert psychiatric evidence.

114.  We are unable to agree with the applicant’s submission that the circumstances of the present case required the Judge to withdraw the charge of murder from the jury. The nature of the defence medical evidence and the serious factual issues raised for the jury’s consideration whether the applicant’s depression “substantially impaired” his mental responsibility for the killing of his wife.

115.  It is fair to say that the defence medical expert was qualified and not unequivocal on matters that went to the element of “substantial impairment”. There were also serious factual issues, which if accepted by the jury, additionally went to the question of “substantial impairment”, such as, the evidence of a financial dispute between the applicant and the deceased; and the conduct of the applicant at the time and after the killing, particularly his efforts in concealing and disposing of his wife’s body and his statements to and dealings with his family members and the police regarding his wife’s disappearance. There was clearly a rational and proper basis for the prosecution to challenge the defence of diminished responsibility.

116.  We are also unable to agree that the Judge failed to sum up the prosecution’s basis for inviting the jury to reject the defence of diminished responsibility.

117.  The Judge unquestionably proceeded to summarise the expert medical evidence accurately and concisely and the prosecution’s challenge to this evidence. She summarised the factors relied upon by the prosecution to the effect that the applicant’s mental responsibility was not substantially impaired and that he knew what he was doing and he was able to form normal judgement.

118.  In the circumstances, the prosecution was plainly entitled to put its case that the partial defence of diminished responsibility did not arise.

119.  The current legislative formulation of the defence of diminished responsibility has been the subject of critical assessment on the general grounds that it is broadly phrased and does not appropriately emphasise the importance of medical evidence. We consider that the current formulation of the defence may benefit from a law reform initiative in examining the terms and reform of the defence in other jurisdictions.

Ground 3: Withdrawal of the psychologist’s evidence on diminished responsibility

120.  Mr Harris submitted that the Judge was wrong to direct the jury to disregard the psychologist’s evidence of Dr Cheng, when considering the issue of diminished responsibility.[144] He acknowledged that he had agreed with the Judge when she stated her intention not to refer the jury to Dr Cheng’s evidence on the issue of diminished responsibility.[145] He said, in hindsight, this was a serious error. As we have already pointed out, the Judge directed the jury on this basis because the defence position was that Dr Cheng’s evidence was only relevant to the issue of provocation.

121.  In support of his submission that Dr Cheng’s evidence was wrongly excluded, Mr Harris relied on the Scottish case of Graham v HM Advocate[146], where it was said that psychological evidence may be admissible and relevant to the issue of an abnormality of mind, although psychiatric evidence was considered likely to be necessary to reach a sufficiency of evidence for this issue to be satisfied, citing another Scottish case of Galbraith v HM Advocate[147].

The respondent’s submission

122.  Mr Lui submitted that in the present case, the cause of the abnormality of mind was the applicant’s depression, a recognised disease of the mind. He argued that the evidence given by Dr Cheng was unrelated to the applicant’s disease of the mind, which could only be established by a medical diagnosis. He relied on HKSAR v Tsang Chiu Tik and Another [148], in which the Court of Appeal held that where the abnormality of mind is said to be “induced by disease”, it would be a matter of medical diagnosis and a witness with no medical qualification is not sufficiently qualified to give expert evidence in this field. As Dr Cheng had explained, clinical psychology was “to understand, assess, deal with and cure or provide treatments to people in relation to their emotion, behaviour, way of thinking and pressure—and stress.”[149] He contended that Dr Cheng was not qualified to testify on matters relating to the applicant’s depression. He noted that Dr Cheng testified on how the applicant had serious issues in emotional control and was susceptible or vulnerable to losing control, more than an ordinary person, which he attributed to the applicant’s workload, ill-health, domestic situation and the deceased’s personality and her psychological abuse of the applicant. He submitted that none of these matters related to the applicant’s disease of mind and even if his evidence revealed some form of an “abnormality of mind” of the applicant, it had no bearing on the particular form of diminished responsibility relied on by the defence at trial.

123.  Mr Lui noted that the relevant observation in Galbraith v HM Advocate was obiter[150] and that such a line of authority had not received “general endorsement” in the United Kingdom or Hong Kong.

Discussion

124.  With respect, we have difficulty with the respondent’s submission as it was clear from Dr Cheng’s evidence that he was addressing the applicant’s psychological state, particularly his loss of self-control, which was a matter that was addressed by the expert psychiatrists on the element of substantial impairment. It is common for psychological evidence to be adduced to support or elaborate upon psychiatric evidence in respect of the defence of diminished responsibility, particularly on the elements of “abnormality of mind” and “substantial impairment”. In our view, whether an accused was suffering from an abnormality of mind was a matter for “medical evidence”, which would require relevant evidence of mental abnormality to be given by a psychiatrist. However, psychological evidence may be admissible and relevant to the defence of diminished responsibility, although as suggested by the Scottish case of Graham, psychiatric evidence would be necessary to reach a sufficiency of evidence to establish an “abnormality of mind”: Graham [151] and Sargeant [152].

125.  The Court of Appeal in Jutting, in accepting the practice that a medical expert may, in appropriate circumstances, give evidence on the ultimate issue of whether or not the accused’s mental responsibility for his act was substantially impaired, acknowledged that this may include evidence from a psychologist.[153] In the discussion, it was noted that the third element of the defence of diminished responsibility was not a purely medical question but a question to which medical evidence may be relevant, but ultimately, it was a question for the jury, having regard to all the evidence.[154]

126.  It is appropriate to note that psychiatrists and psychologists are both practitioners who specialise in the field of mental health, but differ in terms of their learning and practice. Psychiatrists are medical doctors who can diagnose and treat mental health disorders through a combination of therapy, medication and other medical procedures. Psychologists are not medical doctors but trained to diagnose and treat mental health and behavioural disorders through various forms of cognitive and behavioural therapies. There is some obvious overlap in these disciplines, and it is common for a person suffering from a mental health condition to be treated by a psychiatrist or psychologist, or both. They are fields of learning that are related and often complement each other. As noted in Golds, “medical evidence (nearly always forensic psychiatric evidence) has always been a practical necessity where the issue is diminished responsibility.”[155] As experience has shown the partial defence is linked to a recognised medical condition as a matter of practical necessity.

127.  As to when an expert can testify on the ultimate question, it was summarised by Stock JA in HKSAR v Mo Sze Lung Thomson & Another[156]. He said it “depends on the facts of the case; upon the expertise, whether their expertise is relevant to the ultimate question; whether the expert opinion on the ‘ultimate question’ is a conclusion which depends upon his expertise or is proffered in some other capacity; and whether the court requires the assistance of an expert upon the ultimate question.”[157]

128.  Notwithstanding that the Judge gave comprehensive and meticulous directions to the jury on the elements of the offence and the relevant defences, the issue under this ground is whether she was correct in directing them to disregard Dr Cheng’s evidence on the question of diminished responsibility, even though she gave this instruction at the behest of the applicant’s leading counsel.

129.  Some background history of this ground needs to be briefly discussed. In pre-trial proceedings, Mr Harris and Mr Lee sought a ruling from the Judge on the admissibility of Dr Cheng’s evidence. They applied to have his expert evidence adduced into evidence solely in support of the defence of provocation. Whilst prosecuting counsel objected to the admissibility of Dr Cheng’s evidence for this purpose, the Judge ruled it admissible.[158] Later in the proceedings, when the Judge discussed the directions to the jury with counsel, Mr Harris reiterated the defence position that Dr Cheng’s evidence was only relevant to the defence of provocation. Mr Harris also repeated the defence position in his closing address to the jury. He told them that they should only consider Dr Cheng’s expert evidence, “on the issue of provocation alone. Please don’t look at his evidence in relation to diminished responsibility, but on the issue of provocation.”[159]

130.  It is unfortunate that the parties, particularly the defence, did not appreciate the relevance of Dr Cheng’s evidence beyond the issue of provocation. As the medical evidence and the issues unfolded during the course of the trial, it would have been apparent that Dr Cheng’s evidence was relevant to the third element of the defence of diminished responsibility. Mr Harris accepted that he was wrong in taking this approach, submitting Dr Cheng’s evidence was indeed relevant to the issues of abnormality of mind and substantial impairment.

131.  The Judge explained to the jury that it was their responsibility to judge the evidence and decide what was important or unimportant and to consider all the facts of the case that they thought would be relevant and of assistance to them.[160] In her introductory remarks concerning the defences of provocation and diminished responsibility, she stated that the prosecution case was that there was no provocation or substantial impairment of the applicant’s mental responsibility.[161] Whereas, the defence had asked the jury to put weight on the expert opinions in considering the question of diminished responsibility. She said:[162]

“The defence also reminds you that the post-killing conduct of the accused, according to the experts, was not surprising and was consistent with him suffering from depression at the time of the killing. As to the fact that the accused did not seek medical help or did not make any complaint about his condition before the killing, the defence says that there is evidence before you that the accused himself was unaware of his problems at that time and that, according to the experts, it is not uncommon for men to find it difficult to acknowledge their mental issues.

The defence emphasised that the symptoms of weight loss, increased irritability, fatigue, reduced interest in attending meetings with friends, as related to you by Mr Cheng, and reduce memory power, as have been observed by the witnesses, including his children, colleagues and friend. They therefore say that when you address your mind to the question of diminished responsibility you would not fail to find that it is such a case.”

132.  Having referred to the expert opinions, including Dr Cheng’s evidence, the Judge explained to the jury that such evidence provided them with information and opinion that was within the witness’s expertise, and which was likely to be outside their experience and knowledge. She noted that the expert evidence was a part of the evidence to assist them with regard to one or more particular aspects of the case.[163] She concluded by reminding them:[164]

“The expert evidence is just one aspect of the evidence called before you and you should have regard to all the evidence adduced before you before making your findings of fact.”

133.  The Judge then directed the jury on the elements of the defences of provocation and diminished responsibility. She very carefully took the jury through the three elements of diminished responsibility. She instructed the jury according to the standard direction[165] that the applicant had to establish that it was more likely than not:[166]

“(1) that when the accused committed the act which caused his wife’s death, the accused was suffering from an abnormality of mind;

(2) that the abnormality of mind arose from a condition of arrested or retarded development of mind or had an inherent cause or was induced by disease or injury; and

(3) that the abnormality of mind, arising from one or more of those causes, substantially impaired the accused’s mental responsibility for his act which caused his wife’s death.”

She instructed the jury that if the applicant established that the three elements were more likely than not to have been the case, he would be not guilty of murder, but guilty of manslaughter on the basis of diminished responsibility.

134.  In light of the evidence and the position taken by the prosecution, the Judge indicated to the jury that they would have been satisfied to the requisite standard of the first two elements of diminished responsibility, and all that remained was for them to decide the third element. In other words, the issue they had to decide was whether the applicant’s abnormality of mind substantially impaired his mental responsibility for the act of killing his wife.

135.  At this juncture, it is appropriate to refer to the Judge’s remarks when discussing the concept of diminished responsibility. Relevantly, she explained to the jury what was meant by an abnormality of the mind in the following terms:[167]

“… an abnormality of mind simply means a state of mind so different from that of an ordinary human being that a reasonable person would judge it to be abnormal. The expression ‘abnormality of mind’ covers the mind’s activities in all its aspects, not only the perception of physical acts and matters, and the ability to form a rational judgement whether an act is right or wrong, but also the ability to exercise will power to control physical acts in accordance with that rational judgement. … in this case, the abnormality of mind suggested is impairment on the accused ability to form rational judgement and his ability to exercise self-control as a result of his suffering from a depressive episode of moderate to severe severity or major depressive disorder.”

136.  Whilst the meaning of an abnormality of mind follows the specimen direction, its origins lie in the remarks of Lord Parker CJ in R v Byrne [168], which have been endorsed in subsequent decisions. According to the second element of the defence, the abnormality of mind must arise from “a condition of arrested or retarded development of mind or had an inherent cause or was induced by disease or injury”. This is a medical question usually determined by evidence from a psychiatrist.

137.  In the present case, the first two elements were clearly satisfied based on the evidence of the two psychiatrists. The third element, however, was a matter for the jury to decide whether the abnormality of mind substantially impaired the applicant’s mental responsibility for his act, which caused his wife’s death. The third element reverts to the applicant’s abnormality of mind to determine whether his mental responsibility for his act was substantially impaired. This is important because it is a jury question that requires a consideration of all the evidence, but which is not limited to the psychiatric evidence that is usually determinative of the first two elements. However, as already pointed out, a medical expert may, in appropriate circumstances, give evidence on the ultimate issue of whether or not an accused’s mental responsibility for his act was at the time substantially impaired.

138.  The Judge’s directions to the jury on the third element are of considerable relevance in respect of this ground because they reveal the nature and scope of the evidence the jury were instructed to consider regarding substantial impairment. She said:[169]

“… the expression ‘mental responsibility for his acts’ involves consideration of the extent to which his mind was answerable for his physical acts. That includes consideration of the extent of his ability to exercise will power to control those acts. If there was impairment of responsibility, you must consider whether it was a substantial impairment. There is no scientific test which can give you the answer to the question whether the impairment was substantial. Substantial is an ordinary English word which imports a question of degree and to which you will bring your own experience in deciding whether the impairment was substantial in this case without substituting a different word for it.”

139.  The Judge then reinforced her remarks:[170]

“You must approach the question in a broad common sense way. You must ask yourselves, having heard what the medical experts have said and looking at all the evidence, including what the accused did, do we, looking at it broadly as people of ordinary common sense, think it more likely than not that there was a substantial impairment or diminishing or weakening of his mental responsibility, which includes the ability to exercise will power, to control what he did?” (Emphasis added)

140.  After a very comprehensive analysis of the evidence, the Judge turned to consider the medical evidence. She gave an overview of the evidence of the two psychiatrists. She noted that Dr Siu was of the opinion that the applicant was probably suffering from depression and that his ability to form rational judgment and exercise self-control was substantially impaired. Dr Ho was of the opinion that the applicant was likely to be suffering from major depressive disorder, which would have substantially impaired his mental responsibility. As the psychiatric evidence had not been contradicted by the prosecution, the Judge indicated that they would have to have a proper basis to reject their evidence, suggesting that the first two elements of the defence of diminished responsibility had been satisfied. She reiterated that the question of substantial impairment was ultimately a question for the jury, emphasising:[171]

“This is trial by jury, not trial by experts. So approach the question in a broad common sense way by taking into account all the circumstances and all the evidence, not just the medical evidence, although you would no doubt agree that it is important evidence, in answering the question whether the impairment was substantial or not.” (Emphasis added)

141.  The Judge then summarised the psychiatric reports of Dr Siu and Dr Ho, highlighting the following matters. Dr Siu diagnosed the applicant as having a depressive episode of at least moderate severity at the time of the killing[172] and that he presented with prominent symptoms of depression[173]. Dr Ho diagnosed the applicant as suffering from major depressive disorder with at least mild severity[174] and noted that the emotions he was experiencing could lead to violence[175], cognitive impairment[176], and cognitive dysfunctions[177].

142.  The Judge next summed up Dr Cheng’s evidence.[178] He was of the opinion that the applicant might have lost control[179], having suffered chronic psychological abuse at a level of moderate to serious[180]. He explained that this would impact on his ability to control his emotions and lead to a lot of anger and anxiety.[181] He further explained that a person under extreme stress, when his emotions hijacked his rationality, might not be able to focus or recall events afterwards.[182]

143.  Having given the jury careful and detailed directions on the issue of diminished responsibility, the question arises as to whether it was correct or confusing for the Judge to tell them that they were not to take into account Dr Cheng’s evidence on the question of diminished responsibility. She instructed them to exclude Dr Cheng’s evidence in clear and emphatic terms:[183]

“I have one further matter to tell you in relation to the question of diminished responsibility. That is, because diminished responsibility is concerned with abnormality of the mind. So is not something which Dr Cheng, the clinical psychologist, is able to give any opinion. Dr Cheng is not a medical expert. Remember, he is not a medical doctor by profession. He is a clinical psychologist. So on the question of diminished responsibility, do not take into account what Dr Cheng says.”

144.  The Judge added that Dr Cheng’s evidence was relevant to the question of provocation, but as mentioned to them by Mr Harris on behalf of the applicant, they were not to take into account Dr Cheng’s evidence on the question of diminished responsibility.

145.  At the close of her summing-up, the Judge reminded the jury how to deal with the medical evidence. She noted that Dr Siu and Dr Ho testified that the applicant was suffering from depression at about the time of the killing. She said:[184]

“… their evidence is not only relevant to the issue of diminished responsibility, but also relevant to your consideration of the question of provocation because I have set out in the handout for your references to the accused suffering from the depressive episode or major depressive disorder. So for both psychiatrists evidence, especially when the experts mentioned about the ability to control oneself in the reports, those parts are relevant to both questions, that is, the provocation question and also the diminished responsibility question. So do not be mistaken. Do not just take the psychiatrist evidence for consideration in relation to the diminished responsibility issue only. Not only for that, for both questions, diminished and provocation. But you would recall me telling that for Dr Cheng’s evidence, the clinical psychologist’s evidence, that is different because he is not a medical doctor. So you should not take his evidence into account when considering the diminished responsibility question, just in relation to the provocation question, all right.”

146.  The essence of this ground boils down to the following question. Was it correct for the Judge to instruct the jury not to take into account Dr Cheng’s evidence when considering the only issue in respect of the defence of diminished responsibility, namely whether the applicant’s abnormality of mind arising from a major depressive disorder substantially impaired his mental responsibility for the killing of his wife? In our view, it was clearly relevant and should not have been excluded from the jury’s consideration when addressing this aspect of the defence of diminished responsibility.

147.  Dr Cheng explained that clinical psychology seeks to understand, assess and treat people for their emotions, behaviour and stress. He said it could concern issues in respect of the control of emotion, stress from work and marriage, violent acts or issues of memory.[185] From his examination of the background and circumstances of the applicant, he was of the opinion that the applicant was a victim of chronic psychological abuse at a moderate to serious level.[186] He considered that the applicant suppressed his emotions and that his emotional control was low.[187] He said he was not surprised that the applicant could not recall the episode of killing his wife. He explained that for a person under extreme stress, “when his emotion hijacked his rationality”, it may be impossible for him to focus and, therefore, would be unable to recall events.[188]

148.  We consider that the direction to the jury that they exclude Dr Cheng’s evidence from their consideration of the defence of diminished responsibility would, at the very least, have confused them. The defence psychiatric evidence was that the applicant suffered from depression, which affected his ability to form rational judgement and exercise self-control. In similar terms, Dr Cheng’s psychological assessment of the applicant was that he had been subjected to chronic psychological abuse and that this would have impacted on his ability to control his emotions and behave rationally. If the jury were being instructed to ignore Dr Cheng’s evidence on the issue of substantial impairment, which was the only issue they were asked to resolve in respect of the defence of diminished responsibility, then how were they to regard similar evidence from the two psychiatrists? However, in our judgment, Dr Cheng’s evidence was plainly relevant to the third element of diminished responsibility and should not have been excluded from the jury’s consideration.

149.  We come to the issue of whether the exclusion of Dr Cheng’s evidence from the jury’s consideration in relation to the third element of diminished responsibility was a material irregularity that rendered the applicant’s trial unfair.

150.  The Judge instructed the jury that they had to approach the question of whether the applicant’s abnormality of mind substantially impaired his mental responsibility for the killing of his wife “in a broad common sense way.” She stressed that they had to ask themselves, having heard what the medical experts had said and “looking at all the evidence”,[189] did they think it was more likely than not that there was substantial impairment or diminishing or weakening of his mental responsibility, including the ability to exercise will power and control over what he did.[190]

151.  Prosecuting counsel, in his closing address, also emphasised with the jury that on the question of substantial impairment, “it is for you to determine, having considered the whole of the evidence, the whole circumstances and also what had happened before the killing, at the time of the killing and after the killing for you to consider everything then form your view on this matter.”[191]

152.  We are satisfied that the exclusion of Dr Cheng’s evidence from the jury’s consideration on the third element of diminished responsibility constituted a material irregularity that rendered the applicant’s trial unfair.

Conclusion

153.  It followed for the reasons we have given, we granted the applicant leave to appeal against conviction, treated the hearing of the application as the hearing of the appeal, allowed the appeal and quashed the conviction. We refused to invoke the proviso, but considered that in the interests of justice the applicant should be retried on a fresh indictment.

154.  On the question of costs, we directed that the applicant file and serve any written submission within 7 days from the date of the judgment and that the respondent file and serve a written reply within 7 days thereafter.