Using the Defence of Diminished Responsibility in Singapore

One Friday evening, a grandmother strangles her grand-daughter to death after a particularly heated argument. The grandmother had been looking after the grand-daughter since the girl was a baby, along with her two other grandchildren and severely disabled son.

Months before the murder occurred, however, the grandmother suffered from severe mental health issues, stress, and caregiver burnout. Should the grandmother be held fully accountable for the murder, or was her responsibility for killing her granddaughter diminished in some way?

This article explains:

• The defence of diminished responsibility in Singapore
• The difference between the defence of diminished responsibility and unsoundness of mind
• When the defence of diminished responsibility can be raised 
• What happens if the defence of diminished responsibility is successfully raised

What is the Defence of Diminished Responsibility in Singapore?

The defence of diminished responsibility is a partial defence or special exception to the offence of murder under section 300 of the Penal Code in Singapore. It proves that, at the time of the offence, the accused was suffering from a specific abnormality of mind that has:

• Substantially impaired the offender’s capacity to either:
  • Know the nature of their acts or omissions that either caused the death, or in being a party to causing the death; or
  • Know whether such acts or omissions are wrong or against the law; or
• Substantially impaired the offender’s power to control his acts or commissions in causing the death or being a party to causing the death.

If successfully pleaded, the defence of diminished responsibility reduces the criminal liability of a person accused of murder to culpable homicide not amounting to murder.

What is the Difference Between the Defence of Diminished Responsibility and Unsoundness of Mind?

Unsoundness of mind is found under section 84 of the Penal Code, which provides that nothing is an offence if it is done by a person who is:

• Incapable of knowing the nature of the act committed;
• Incapable of knowing that what he is doing is wrong or against the law; or
• Has completely no control over his actions.

The defence of diminished responsibility hence differs from unsoundness of mind in the following ways:

The mental condition and state of the accused 

Unsoundness of mind suggests a complete incapacity or the total inability of the accused to know that his actions are wrong or against the law, or to control them.

On the other hand, the defence of diminished responsibility suggests only a diminished, or partial, incapacity at the time of commission of the offence.

The accused, in this case, still retains the mental capacity to know both the nature and wrongfulness of his act. However, he had been suffering from a mental condition that substantially impaired – as opposed to fully impaired – his mental state when he committed the act in question.

The offences for which the defence applies 

While the defence of diminished responsibility applies as a defence to only the offence of murder, unsoundness of mind can be applied to not just murder but other criminal offences as well.

The effect of a successful defence

An accused person who successfully pleads unsoundness of mind will not be held criminally liable or accountable for the offence that was committed, and he may be acquitted.

However, if the court finds that the accused would have been found guilty of committing the offence if he had not been suffering from an unsound mind, the accused will be placed in safe custody and undergo treatment to ensure that he will not present a danger to himself or to other persons when he is released.

For more on the defence of unsoundness of mind in Singapore, you may refer to our other article on this subject.

On the other hand, an accused person who successfully raises the defence of diminished responsibility will still be held criminally liable for the offence that was committed. However, his charge will be reduced to one of culpable homicide not amounting to murder under section 304 of the Penal Code instead.

Learn more about the differences between murder and culpable homicide not amounting to murder in our other article.

When Might an Accused be Able to Raise the Defence of diminished Responsibility?

In the case of Public Prosecutor v Boh Soon Ho, the Singapore High Court affirmed that the following three cumulative conditions must be satisfied for an accused person to raise the defence of diminished responsibility:

1. The accused was suffering from an abnormality of mind.
2. The abnormality of mind must have resulted from either of the following:
   • A condition of arrested or retarded mental development;
   • Any inherent causes (e.g. depression; or
   • The result of a disease or injury.
3. The abnormality of mind resulted in the substantial impairment of the accused’s mental responsibility for their acts.

The cause of the abnormality of mind – the second condition – is a fact that is largely determined by expert medical evidence, while the first and third conditions are facts that must be determined by the courts.

As these are cumulative conditions, all three of them must be met before an accused person can successfully raise the defence of diminished responsibility. For example, if the court finds that the accused had not been suffering from an abnormality of mind (i.e., the first condition), then it would not need to go on to deal with the other conditions.

In cases where the defence of diminished responsibility has been raised, the courts have tended to focus on the connection between the accused person’s abnormality of mind and his responsibility for the offence. In particular, the requirement of substantial impairment means that there must be “a real and material impairment of the accused’s mental state”.

Medical evidence is important in helping the courts determine the presence of such an impairment and the severity of it. However, the courts have stressed that it would be sufficient to show that the substantial impairment influenced the accused person’s actions. It is not necessary to show that the substantial impairment caused the offence to be committed.

The following cases are examples of how the courts have applied this approach in determining whether the defence of diminished responsibility applies:

Defence of diminished responsibility succeeded as accused’s major depressive disorder substantially impaired his ability to think rationally

In June 2021, an accused who had slashed his boss to death, and attacked two other bosses after he was fired, was sentenced to 20 years’ imprisonment for one charge of culpable homicide not amounting to murder, and another charge of voluntarily causing grievous hurt by a dangerous weapon.

In this case, the High Court noted that at the time when he had committed the offences, the accused was suffering from a major depressive disorder, which substantially impaired his ability to think of a more rational solution to dealing with the issue of him getting fired.

As a result, the accused responded and reacted in a violent manner by attacking his bosses with weapons to severely injure them.

Defence of diminished responsibility did not succeed as accused’s adjustment disorder did not impair his mental responsibility 

In another case, a foreign worker who was sentenced to death in December 2020 for strangling his girlfriend claimed that she had humiliated him right before he killed her. The accused raised the defence of diminished responsibility by submitting that he had been suffering from an adjustment disorder – a stress-related mental health condition – at the time of committing the offence, which impaired his mental responsibility for the killing.

However, the High Court rejected the accused’s defence. Although psychiatric experts for both the prosecution and defence agreed that the accused was suffering from an adjustment disorder when he committed the offence, the High Court noted that the accused was able to continue working and performing well in his job and pursue recreational activities.

The court also found that his ability to make decisions and exercise self-control were not impaired. Accordingly, it found no impairment in his mental responsibility for his acts.

What Happens If an Accused is Able to Successfully Prove Diminished Responsibility? 

The defence of diminished responsibility provides for a measure of criminal liability or accountability for accused persons who kill. However, it also recognises that it was their substantially impaired mental capacity that had led them to kill.

If an accused person successfully raises the defence of diminished responsibility, his criminal liability is reduced, and he will be convicted instead with the offence of culpable homicide not amounting to murder.

In this case, where the accused had acted with an intention to cause death or of causing bodily injury that is likely to cause death, the accused will be sentenced to either life imprisonment and caning, or imprisonment for a term of up to 20 years, as well as a fine or caning.

Where there had been no intention to cause death, but the accused had caused death or bodily injury while knowing that the act was likely to cause death, the accused will be sentenced to a term of imprisonment of up to 15 years, a fine and/or caning.

However, an accused person who unsuccessfully raises the defence of diminished responsibility can be convicted of murder and then sentenced to either the death penalty, or life imprisonment and caning, depending on the seriousness of their acts.

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Diminished responsibility is a partial defence to the offence of murder. As discussed above, a person accused of murder seeking to rely on this defence must be able to satisfy its requirements, else risk the defence being rejected and themselves being convicted of murder.

If you have been charged with murder and wish to raise the defence of diminished responsibility, it is best to consult a criminal lawyer for further advice. The offence of murder is a very serious crime that carries a severe penalty, and legal advice could mean the difference between you receiving a term of imprisonment or the death penalty.

You may get in touch with experienced criminal lawyers here.