Changes to the Defence of Mental Illness (NSW)

Where a person is suffering from a mental illness or cognitive impairment at the time of committing an offence, with that impairment being so significant that the person did not know their actions were wrong, or did not know the nature and quality of their actions, they may be able to rely on the defence of mental or cognitive impairment (previously known as the defence of insanity). 

The Act and the Test:

The Mental Health and Cognitive Impairment Forensic Provisions Act 2020 at Section 28 provides that a person is not criminally responsible for an offence if, at the time of carrying out the offence, the person had a mental or cognitive impairment (or both) that had the effect that the person:

1. Did not know the nature and quality of the act, or 
2. Did not know that the act was wrong (that is, the person could not with a moderate degree of sense and composure about whether the act, as perceived by reasonable people, was wrong).

Definitions:

The Act provides in Section 4 that a person has a “mental health impairment” if:

• The person has a temporary or ongoing disturbance of thought, mood, volition, perception or memory, and 
• The disturbance would be regarded as significant for clinical diagnostic purposes, and 
• The disturbance impairs the emotional wellbeing, judgment or behaviour of the person. 

Where a person’s actions are caused solely by temporarily ingesting a substance or a substance use disorder, they do not have a “mental health impairment” for the purpose of the Act. 

The Act provides at Section 4 that a person has a “cognitive impairment” if:

• The person has an ongoing impairment in adaptive functioning, and 
• The person has an ongoing impairment in comprehension, reason, judgment, learning or memory, and 
• The impairment results from damage to or dysfunction, developmental delay or deterioration of the person’s brain or mind that may arise from the below conditions or for other reasons.

A cognitive impairment may arise from the following conditions but may also arise for other reasons:

• Intellectual disability, 
• Borderline intellectual functioning,
• Dementia, 
• An acquired brain injury, 
• Drug or alcohol related brain damage, including foetal alcohol spectrum disorder, 
• Autism spectrum disorder. 

Principles:

Prior to the introduction of the Act, the defence of mental illness or insanity was derived from case law in the matter of M’Naughten [1843-1860] All ER Rep. This case defined insanity as “a defect of reason, disease of the mind, as not to know the nature and quality of the act the Defendant was doing; or if he did know it, that he did not know what he was doing was wrong”. This definition and the principles of this case were codified in legislation when the Act was introduced in 2020.  

The Act states that until the contrary is proved, it is presumed that the Defendant did not have a mental health impairment nor cognitive impairment. If a Defendant is relying on the defence of mental or cognitive impairment, they bear the factual and legal burden to prove their impairment to the standard of the balance of probabilities. 

Whether a person has a mental or cognitive impairment is a question of fact. This means that the jury or Judge is required to decide whether the Defendant had a mental health or cognitive impairment and whether such impairment meant the Defendant did not know the nature, quality or wrongness of their actions. 

When the Prosecution and Defendant agree on the impairment, Section 31 of the Act allows the Court to enter a special verdict of act proven but the Defendant not criminally responsible at any times during the proceedings if both parties agree that the proposed evidence establishes an impairment, the Defendant is legally represented and the Court is satisfied that the defence is so established. 

If it is accepted that the Defendant had an impairment and the impairment was such that they did not know the nature and quality of their actions or did not know that the act was wrong, the jury will be directed to return ‘special verdict’ that they find the act proven but the person is not criminally responsible by reason of that impairment. 

These kinds of proceedings can still result in significant consequences for the accused person. Instead of being found guilty and sentenced according to normal criminal law penalties, persons can be detained in mental health facilities, sometimes, indefinitely. You can read more about Special Hearings here. 

If you have been charged with an offence and had a mental health or cognitive impairment, we recommend you speak with one of our lawyers as soon as possible.