Under s 23A Crimes Act 1900, a partial defence to murder is available on the basis that the offender lacked the capacity ‘to understand events, or to judge whether the person’s actions were right or wrong, or to control himself or herself’ because of mental health or cognitive impairment.
If proved, the defence reduces the charge of murder to manslaughter.
This partial defence is known as diminished responsibility or substantial impairment.
What is mental health or cognitive impairment?
A mental health impairment is defined in s 4C of the Crimes Act 1900 as a temporary or ongoing disturbance of thought, mood, volition, perception or memory’. This disturbance must be significant enough for clinical diagnostic purposes and must impair the emotional wellbeing, judgment or behaviour of the person.
Some examples include an anxiety disorder, clinical depression, bipolar disorder, a psychotic disorder or a substance induced mental disorder that is not temporary.
Cognitive impairment is defined in s 23A(8) of the Crimes Act 1900 is an ongoing impairment in adaptive functioning. The ongoing impairment must affect a person’s comprehension, reason, judgment, learning or memory and result from damage, dysfunction, developmental delay or deterioration of the person’s brain.
Some examples include intellectual disability, dementia, an acquired brain injury, drug or alcohol related brain damage or autism spectrum disorder.
Difference between ‘Diminished responsibility’ and ‘Defence of mental health impairment or cognitive impairment’
The Mental health and Cognitive Impairment Forensic Provisions Act contains a general defence to criminal responsibility by way of mental illness or cognitive impairment. The most significant difference between these two defences is the scope of criminal acts the defence is available for.
As discussed, diminished responsibility is only available for murder, and if successful is only a partial defence reducing the charge from murder to manslaughter.
A defence by way of mental illness or cognitive impairment is available for all criminal charges and is a full defence, meaning that if successful an accused person is not guilty of the offence.
The required nexus between the offending behaviour and the accused mental illness or cognitive impairment is also higher than that of diminished responsibility, requiring the accused to ‘not know the nature and quality of the act, or not know the act was wrong’.
Intoxication
By way of s 23A(3) Crimes Act 1900, self-induced intoxication at the time of offence and the effects of that self-induced intoxication must be disregarded when determining whether an accused person had a lack of capacity ‘to understand events, or to judge whether the person’s actions were right or wrong, or to control himself or herself’.
The Test
Diminished responsibility is made out if the following two criteria are satisfied:
- If at the time of the conduct, an accused’s capacity to understand events, or judge whether their actions were right or wrong, or to control themselves, was substantially impaired by a mental health impairment or cognitive impairment; and
- The mental health impairment or cognitive impairment was substantial as to warrant liability for murder being reduced to manslaughter.
The second part of this test often involved a qualitative assessment for the jury in a murder trial.
Burden of Proof
The determination of diminished responsibility is on the balance of probabilities and the accused bears the onus of proof.
Should you or someone you know be charged with an offence, it is essential you receive legal advice from an experienced criminal defence lawyer at any early stage. To discuss your options, call Hugo Law Group in Sydney, NSW (02 9696 1361), Canberra (02 5104 9640) or Perth (08 6255 6909) to make an appointment to speak to one of our lawyers.
