What were the facts of CNK v Public Prosecutor [2024] SGCA 42?

On 19 July 2021, a 16-year-old Secondary 4 student, referred to as CNK and suffering from major depressive disorder, fatally attacked 13-year-old schoolmate Ethan Hun Zhe Kai with an axe at River Valley High School as part of a "suicide by cop" plan.

[2024] SGCA 42 — CNK v PUBLIC PROSECUTOR

Q: Why was CNK not convicted of murder in [2024] SGCA 42?

The Prosecution was satisfied that, because CNK was suffering from major depressive disorder at the relevant time, he was entitled to the partial defence of diminished responsibility, so his charge, initially one of murder, was reduced accordingly.

SUPREME COURT OF SINGAPORE

23 October 2024

Case summary

CNK v Public Prosecutor [2024] SGCA 42

Criminal Appeal No 21 of 2023

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Decision of the Court of Appeal (delivered by Chief Justice Sundaresh Menon):

Outcome: The court dismisses the offender’s appeal and upholds the sentence of 16 years’ imprisonment, finding that the offender’s major depressive disorder can only attenuate his culpability to a limited extent.

Background

1 On 19 July 2021, a fatal axe attack occurred at River Valley High School (“RVHS”). A 16-year-old Secondary 4 student killed his schoolmate, Ethan Hun Zhe Kai (whom the court refers to as “Ethan” or the “deceased”), a 13-year-old Secondary 1 student, in a male toilet in RVHS by repeatedly slashing him on his head, neck and body with an axe, with the intention of causing death. At the point of the killing, the offender, who was a minor and whom the court refers to as “CNK”, was suffering from major depressive disorder (“MDD”). CNK did not know Ethan. He killed Ethan as part of his plan to commit “suicide by cop”, which was a tragically ill-conceived plan to go on a killing spree that he thought would lead to the police being activated and being left with no choice but to shoot and kill him.

2 The Prosecution was satisfied that on account of CNK suffering from MDD at the relevant time, he was entitled to the partial defence of diminished responsibility. As a result, CNK, who had initially been charged with murder, had that charge reduced to a charge of culpable homicide not amounting to murder punishable under s 304(a) of the Penal Code (Cap 224, 2008 Rev Ed) (“Penal Code”) and he pleaded guilty to this.

3 CNK was convicted and sentenced to 16 years’ imprisonment by a judge of the General Division of the High Court (the “Judge”).

4 This is his appeal against sentence. An important issue in this appeal is the extent to which CNK’s MDD might attenuate his culpability for the purposes of sentencing.

5 The court dismisses the appeal and upholds the sentence of 16 years’ imprisonment.

Decision on appeal

The relevance of mental conditions to sentencing (as distinct from the partial defence of diminished responsibility)

Diminished responsibility

6 To rely on the partial defence of diminished responsibility, an offender bears the burden of proving three cumulative requirements:

a. first, that he was suffering from an abnormality of mind;

b. second, that the abnormality of mind: (i) arose from a condition of arrested or retarded development of mind; (ii) arose from any inherent cause; or (iii) was induced by disease or injury; and

c. third, the abnormality of mind substantially impaired his mental responsibility for his acts and omissions in relation to his offence: at [59].

7 In respect of the first requirement, “abnormality of mind” refers to a state of mind so different from that of ordinary human beings that the reasonable man would term it abnormal. This is wide enough to encompass the mind’s activities in all its aspects, including an abnormally reduced mental capacity to (a) understand events or perceive physical acts and matters; (b) judge the rightness or wrongness of one’s actions; or (c) exercise self-control over one’s actions. The existence of an abnormality of mind is to be determined by the trial judge as a matter of fact: at [60].

8 The second requirement relates to the aetiology of the abnormality, which is a matter largely to be determined based on expert evidence. The prescribed aetiologies ought to be read restrictively rather than extensively, such that the partial defence of diminished responsibility would only apply to accused persons suffering from recognised and established psychiatric conditions, and would exclude abnormalities of mind that arise from other sources, such as heightened states of emotion or intoxication, that are not beyond the accused person’s control: at [61].

9 In relation to substantial impairment under the third requirement, the abnormality of mind must have had a real and material (as opposed to trivial or minimal) effect or influence on the offender’s mental responsibility for his acts and omissions in relation to the offence. This is largely a question of commonsense to be decided by the trial judge as the finder of fact. What is required is an impairment of the mental state that is real and material, as opposed to trivial or minimal, but which need not rise to the level of amounting to the defence of unsoundness of mind. The offender’s abnormality of mind need not be the cause of his offending; it is sufficient for the abnormality of mind to have had an influence on the offender’s actions: at [62].

10 There are typically three ways in which a mental condition may substantially impair a person’s mental responsibility: (a) where it affects the person’s perception of physical acts and matters; (b) where it hinders the person’s ability to form a rational judgment as to whether an act is right or wrong; and (c) where it undermines the person’s ability to exercise his or her will to control physical acts in accordance with that rational judgment. The categories of factors that may impair mental responsibility are not closed and it is, in principle, open to an offender to contend that there was substantial impairment by reference to other categories of mental capability and responsibility: at [63].

11 An accused person who commits a premeditated murder may yet be able to prove that his abnormality of mind had substantially impaired his mental responsibility by demonstrating that it impaired his rationality in coming to the decision to commit the murder. In such a situation, although the accused person knows what he is doing, and to that extent has control over his conscious and deliberate actions, these actions are to carry out a decision that is the product of a disordered mind, which is not functioning rationally. In such cases, where the accused person premeditates to kill under a veneer of rationality, but the decision to kill is in essence the product of his disordered mind, two further requirements must be met to avail of the partial defence of diminished responsibility: (a) the accused person must show that but for his abnormality of mind, he would not have made that decision; and (b) the accused person must prove on a balance of probabilities that in executing his intention to murder, he had no realistic moment of rationality and self-control that would have enabled him to resile from that intention or plan: at [64]–[65].

12 However, where it is the offender’s ability to assess the risks that inhere in offending that is impaired, such impairment does not amount to a substantial impairment of one’s mental responsibility so as to give rise to the partial defence of diminished responsibility. An impairment in one’s ability to assess risk does not affect one’s ability to comprehend the nature or wrongfulness of one’s actions or one’s ability to control one’s physical acts. While an impairment of one’s ability to assess risk might make it more likely that one will decide to commit the offence, this is born out of the mistaken belief that one is likely to be able to get away with the commission of the offence. The mistaken assessment of the risk calculus cannot be a basis for invoking the partial defence of diminished responsibility: at [67].

13 At the stage of deciding whether the partial defence of diminished responsibility is available, the question is a binary one: did the mental disorder of the sort contemplated by the legislation substantially impair the accused person’s mental responsibility? If the answer to the question is in the negative, then there will be little, if any, room to further consider the offender’s mental condition. If the answer to the question is in the affirmative, then the offender’s charge will be reduced to one of culpable homicide not amounting to murder and the court will then have to decide on the appropriate sentence for the offender. In exercising its discretion, it will be relevant for the sentencing court to revisit the offender’s mental condition and specifically to examine the extent to which it reduces his culpability: at [70]–[71].

Sentencing

14 The specific inquiries the court should undertake in determining the impact that the offender’s mental condition would have on sentencing are as follows:

a. the existence, nature and severity of each mental condition;

b. where there are multiple mental conditions, the interaction between them and in particular, the synergistic manner in which different mental conditions may come together and operate on the accused person’s mind;

c. whether a causal link can be established between the conditions and the commission of the offence;

d. the extent to which the offender had insight into his mental conditions and their effects; and

e. whether the overall circumstances are such as to diminish the offender’s culpability, and if so, to what extent.

Evidently, some of these inquiries may not arise in some cases. But as a general guide, the court considers that this is a useful framework for addressing the impact of a mental condition on the calibration of the sentence: at [73] and [75].

15 In particular, the third inquiry concerns the critical issue of causality. The court should assess the impact that the offender’s mental condition had on his mental responsibility, having regard to (a) the offender’s basic cognitive ability to perceive his acts and know their nature; (b) the offender’s moral and legal cognition to know and appreciate the wrongfulness of his acts; and (c) whether the offender was able to exercise his will to control his actions. While this is not an exclusive or exhaustive set of factors, these are the ones most commonly considered. The weaker the link between the offender’s mental condition and his decision to commit the offence, the less weight this will have in the sentencing matrix. Where there is no causal link, the fact that the offender was suffering from a mental condition will generally be irrelevant to sentencing: at [74].

16 Elements of this framework do overlap with the factors to be considered for the purposes of assessing the availability of the partial defence of diminished responsibility. This is unsurprising because the latter is a threshold inquiry, but once it has been crossed, it remains a necessary step for the court to go further and undertake a distinct inquiry into the extent to which the offender’s culpability and moral responsibility for the offence was affected or impacted by his mental condition. The moral culpability of mentally disordered offenders lies on a spectrum, and the nature and gravity of the offender’s mental condition and its impact on the commission of the offence must be carefully considered in each case: at [76]–[78].

17 The court will also have regard to other considerations aside from the offender’s mental condition that may aggravate or mitigate the offender’s culpability: at [79].

Culpable homicide sentencing precedents

18 While offences of culpable homicide under s 304(a) of the Penal Code are committed in a wide variety of circumstances, the court broadly categorises the culpable homicide precedents involving an operative mental impairment on the part of the offender, in an attempt to rationalise the precedents and explain which of these may be relevant to a given type of case, and why. The court identifies the following broad categories with their corresponding typical sentencing ranges: at [133].

a. Cases where the offender was labouring under a mental disorder satisfying the test articulated in the case of R v Rowland Jack Forster Hodgson (1968) 52 Cr App R 113 (hereinafter, the “Hodgson criteria”) – life imprisonment. Inherent in the Hodgson criteria is the likelihood of reoffending behaviour on account of the offender’s unstable mental condition, coupled with the grave consequences of such behaviour. In such circumstances, the protection of the public is the foremost consideration, and this justifies the imposition of a sentence of life imprisonment.

b. Cases where the offender had been repeatedly violent and/or physically abusive leading up to the death of the victim – upper end of the range approaching 20 years’ imprisonment. Where the circumstances of the offence feature a high degree of violence, cruelty and inhumane treatment of the victim over a period of time, the sentencing range tends to approach 20 years’ imprisonment, second only to the maximum sentence of life imprisonment, and this step down is typically justified by the mitigating weight of the offender’s mental condition.

c. Cases where the killing was premeditated and brutal – upper end of the range, typically around 18 to 20 years’ imprisonment. Where premeditation is the principal factor in a case, a sentence at the high end of the sentencing range would be warranted. If the offence also features an element of brutality or cruelty, the sentence will tend towards the highest end of the range approaching 20 years’ imprisonment.

d. Cases where the attack was spontaneous and unplanned – between ten and 18 years’ imprisonment. The range should typically be more than ten years’ imprisonment, with reference to the two categories of cases that follow, where the offender’s culpability is demonstrably reduced as a result of the offender’s mental impairment, but would ordinarily not exceed the sentencing range for premeditated and brutal killings typically attracting 18 to 20 years’ imprisonment.

e. Cases where the offender was suffering from a mental condition that distorted his sense of reality at the material time – typically a lower range of six to nine years’ imprisonment. In these cases, the offender’s mental condition is so severely impaired that it significantly diminishes his culpability. At the same time, the court is concerned with the prevention of harm to protect the public such that a substantial imprisonment term is nonetheless warranted.

f. Cases where parents afflicted by a mental condition kill their children as a result – typically a lower range of five to seven years’ imprisonment. These cases fall under two sub-categories: the first is where the parent was motivated by a misguided view of what was best for their child as a result of serious mental impairment, coupled with a sense of despair; the second is where the parent kills the child out of frustration or loss of control, brought about by a mental affliction that led the parent down the tragic path of taking their child’s life.

Facts of the present case

Circumstances of the offence

19 CNK exhibited a chilling degree of premeditation and a cold and calculated approach in planning and preparing for the killing. From as early as five months prior to the offence, he had researched the internet for a suitable weapon and picked a machete or axe because it would be suitable for an inexperienced user. He then tested the sharpness of the weapons, and when he was not convinced of their lethality, arranged to have them sharpened. He examined the floor plan of RVHS ahead of the attack to plan how best he could carry out the attack. He also decided on a school slashing because he was older than most of the other students and thus was more likely to secure his goal. A month prior to the killing, he prepared for the knife attack by seeking out online videos depicting actual scenes of human deaths and killings, termed “snuff” videos, to educate himself on the most efficient way of killing his prospective victim. He taught himself how to grip the axe properly from the internet. The degree and extent of planning and preparation that was undertaken by CNK went well beyond that seen in most of the precedents: at [135].

20 Based on CNK’s poems titled “Liberation” and “_Liberated_”, which alluded to mass killings conducted in a school, CNK appeared to be enthralled by the idea of a school killing and the notoriety it could bring him. The Judge was entitled to draw the inferences relating to CNK’s psyche, specifically that he found the idea of a school killing “appealing”, from the contents of the poems. The Judge was making an inference of fact and it was not necessary for her to be assisted by expert advice in order to be able to do this. Further, the Judge viewed the poem in the context of the facts and circumstances surrounding the killing in arriving at her conclusion: at [136].

21 Aside from the degree of premeditation that was involved, this case also featured a high degree of brutality and callousness, and the targeting of a wholly innocent, defenceless young victim who just happened to be at the wrong place at the wrong time. Leaving aside CNK’s youth and notwithstanding his mental impairment, the starting sentence would have been around 20 years’ imprisonment: at [137].

The effect of the appellant’s MDD

22 CNK suffered from MDD of moderate severity for about six months leading to his offence. He felt life was worthless and started to entertain thoughts of death. He felt that there was no way out of his life predicament other than by committing suicide. However, CNK could not bring himself to commit suicide and decided to “let someone do [it] for [him]”. He learnt from the internet that if he were to kill others he could get himself killed by the police, and decided to embark on this avenue: at [139].

23 CNK’s MDD clearly led to his seriously considering suicide, and it limited his perception of the alternative courses open to him. This contributed to his irrationality in choosing to commit suicide by cop; but for his MDD, he would not have come to that decision. He did not have any realistic moment of rationality and self-control that would have enabled him to pull back from his plan. For these reasons, CNK would have qualified for the partial defence of diminished responsibility had that been an issue for the court’s determination. However, it remains necessary to assess the extent to which CNK’s culpability can be attenuated in light of his mental impairment, in order to calibrate the sentence: at [140]–[141].

24 While CNK’s MDD undoubtedly contributed to the killing, there were also other contributory factors at play, as set out in the psychological and psychiatric reports. This includes, in particular, his consumption of snuff videos which he knew was “pervers[e] and abnormal”, and which ultimately worsened his callousness, desensitised him, and removed the psychological obstacles involved in taking someone’s life in an axe/knife attack. He also did not at any time seek help for the despair he felt: at [143].

25 Despite his MDD, CNK still retained a significant degree of rationality. Although CNK was ultimately mistaken as to the viability of suicide by cop in Singapore, CNK was not acting on the basis of fantasy or fiction. It was not beyond reason nor was it delusional to conceive that the police might shoot him had he gone on a killing spree in RVHS. His thought process was logical, and his plan was carefully and meticulously thought out. The killing was founded on a rational factual basis, albeit he may have been mistaken about the viability of his method of suicide by cop: at [144].

26 CNK knew the nature and wrongfulness of his acts, knew that suicide by cop was legally and morally wrong, and wrestled with some ambivalence over it for a few months. His depression did not undermine his ability to wilfully control physical acts to materialise this plan. In fact, he appreciated the physical damage required to increase the chances of death, and methodically prepared for the axe attack: at [145].

27 For these reasons, CNK’s MDD can only attenuate his culpability to a limited extent: at [146].

Sentencing considerations

28 Given the heinous nature of the offence and the fact that CNK’s culpability remained on the high end of the spectrum, retribution is the foremost sentencing consideration in this case. In the case of offenders who retain a degree of rationality and evince the ability to think logically and coherently, borne out by a sophisticated degree of planning and premeditation, their mental disorder can only ameliorate their culpability to a limited extent, and retribution and deterrence should nonetheless feature as dominant sentencing principles. Where the offence is particularly serious or heinous, there is no reason why retributive principles of sentencing should not prevail over the principle of rehabilitation, notwithstanding the offender’s mental disorder or his youth: at [147]–[149].

29 General deterrence also applies in the present case to deter persons similarly situated as CNK, meaning those suffering from a mental condition but still retaining the capacity to comprehend the wrongfulness of their actions, from consciously indulging in their thoughts and inclinations (which they recognise to be perverse and wrong) and taking active steps to turn those thoughts into reality. The other two contributing factors, namely, CNK’s refusal to receive external help and his consumption of snuff videos, were within his control and therefore should be seen as susceptible to deterrence: at [151].

30 The Judge was fully cognisant that rehabilitation ought generally to be the dominant sentencing consideration in cases involving young offenders, and that the fact that CNK was labouring under a serious mental disorder was a significant countervailing factor against placing retribution, instead of rehabilitation, as the predominant sentencing principle. Ultimately, considering all the circumstances and the high level of CNK’s moral culpability, the Judge decided that retribution should prevail. There is no reason to interfere with the Judge’s exercise of her sentencing discretion: at [152].

Whether the Judge took into account remission for good behaviour when calibrating the length of sentence

31 CNK is plainly wrong to assert that the Judge had taken into account the factor of remission for good behaviour when calibrating the length of sentence. This did not feature as a consideration in the Judge’s calibration of the sentence: at [158].

This summary is provided to assist in the understanding of the Court’s grounds of decision. It is not intended to be a substitute for the reasons of the Court. All numbers in bold font and square brackets refer to the corresponding paragraph numbers in the Court’s grounds of decision.

CNK v PUBLIC PROSECUTOR

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Summary

What were the facts of CNK v Public Prosecutor [2024] SGCA 42?

Why was CNK not convicted of murder in [2024] SGCA 42?

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