Substantial Impairment by Abnormality of the Mind– A Partial Defence to Murder

In Regina v Malcolm Robert Potts, a 33 year old NSW man with schizophrenia stabbed his father to death with a knife in what the court said appeared to have been a “frenzied attack.” In evidence at the trial, Dr Olav Nielssen, psychiatrist, expressed the opinion that the offender’s behaviour was attributable to an abnormal state of mind because he was in the early phase of a relapse into his mental illness.

He was on a regime of anti-psychotic medication at the time but the dosage was relatively low. In addition, he was using cannabis and there was evidence that it could reduce the effect of the medication. It appears from his psychiatric history that he had engaged in irrational and aggressive behaviour during previous exacerbations of his illness. Some of that behaviour had also been directed to his father.

The central issue of the case was substantial impairment under s23A of the Crimes Act. The court found it unlikely he would again act in such a violent matter. He was found guilty of manslaughter and received a slightly reduced sentence because his condition.

What Makes a Killing a Murder?

To find someone guilty of murder the following must be proven:

• The death of the victim
• Caused by an act or omission of the accused
• There was no lawful cause or excuse for the act
• The accused performed the act or omission causing death
• The accused intended to kill or do grievous bodily harm
• The accused should have foreseen death was probable as a result, or in the commission of another serious indictable offence

If anyone of these elements are missing, there can be no conviction for murder.

Mens Rea

In law, mens rea (Latin for “guilty mind”) describes the state of mind of the defendant at the time a crime is committed. Only a defendant who was sufficiently aware of their actions and the possible consequences can choose to behave in the criminal manner and satisfy the intent element of murder. A lack of mens rea is the basis of several criminal defences.

If a defendant did not understand what he or she was doing at the time of the crime, a murder conviction may be reduced to manslaughter, which generally carries a lighter sentence.

An Abnormality of the Mind

An abnormality of mind is a state of mind that is so different from what ordinary human beings experience that a reasonable person would easily identify it as abnormal. There are scads of maladies that might fall under the partial defence of substantial impairment defence.

However, in all cases, the impairment caused by the illness or condition must have been severe enough to cause substantial impairment.

The Substantial Impairment by Abnormality of the Mind Murder Defence

Despite some similarities, substantial impairment by abnormality of the mind is not the same as the insanity defence. Sometimes referred to as diminished responsibility, it is a partial defence to murder. It does not excuse the act, it only reduces the level of crime. Additionally, substantial impairment does not include self-induced intoxication.

A defendant must prove that the defence applies to his or her case. Under Section 23A of the Crimes Act (1900), substantial impairment by abnormality of mind, a person otherwise guilty of murder should instead be convicted of manslaughter if:

• An abnormality of the mind caused by an underlying condition impaired them so that when the act occurred, they did not have the ability to:
  • Understand events
  • Judge their actions as right or wrong, or
  • Control themselves
• The impairment was substantial enough that their liability for murder should be reduced to manslaughter. (Source: Judicial Commission of New South Wales).

Underlying conditions are pre-existing mental or physiological conditions. They are notable and hard to ignore, and are not transitory. Proving that an underlying condition existed usually requires the testimony of medical professionals. An underlaying condition is not necessarily a “disease of the mind” as required for an insanity defence. The important issue is whether a defendant was so impaired that they should receive a manslaughter conviction instead of a murder conviction.

Proving an underlying condition existed may support claims that when the act occurred, the defendant was incapable (and thus did not have the ability or capacity to understand or make judgements about the rightfulness or wrongness of their actions or to control themselves.

Substantial Impairment Defence in NSW Courts

In R. v Zano, the defendant stabbed his friend after a night of drinking. At trial he did not dispute that he was guilty of manslaughter. While issues of mental illness and lack of intent were raised, the jury considered whether the offender should be found guilty of manslaughter due to the defence of substantial impairment. His conviction and sentence were upheld on appeal.

Some courts take a more jaded view of the defence. In Catley v R, a man beat and then stabbed his mother to death. The jury reduced the offence of murder to manslaughter. The jury believed that at the time of the crime, the defendant was suffering from an abnormality of mind that “…substantially impaired his capacity to understand events, or judge whether his actions were right or wrong, or to control himself.”

However, the judge was less convinced of the defendant’s claim of suffering from psychosis. He did accept that the defendant suffered from an abnormality of mind arising from an underlying condition due to depression, paranoid-type symptoms and possible psychosis, but “…doubted that “any psychosis the offender has suffered or continues to suffer played a very great part in the commission of the offence.” (R/S [37]).

Push Back Against the Defence

Courts and citizens often seem wary of the substantial impairment by abnormality defence, perhaps with good reason. Not all jurisdictions in Australia allow for the substantial impairment defence, only New South Wales (‘NSW’), Queensland, the Australian Capital Territory (‘ACT’), and the Northern Territories. There is an argument in NSW that, instead of using this defence, courts can address the same issues during sentencing. Nonetheless, criminal law must include allowances for those afflicted with underlying conditions that may affect their ability to separate right from wrong.