Published by Geoff Harrison | 22 December 2024
Section 23A of the Crimes Act 1900 provides a partial defence to murder of substantial impairment because of mental health impairment or cognitive impairment. It was previously termed substantial impairment by abnormality of mind but was amended with effect from 27 March 2021 by the Mental Health and Cognitive Impairment Forensic Provisions Act 2020.
“Mental health impairment” and “cognitive impairment” are defined in ss 4C and 23A(8) respectively of the Crimes Act 1900. They are in identical terms to the definitions in ss 4 and 5 of the Mental Health and Cognitive Impairment Forensic Provisions Act 2020 (cited in Criminal Trial Courts Bench Book at 6-550).
Other Sources:
Public Defenders: Partial Defences to Murder, Provocation and Diminished Responsibility
NSW Law Reform Commission Report 82 (1997) – Partial Defences to
Crimes Amendment (Diminished Responsibility) Act 1997 No 106
Partial Defences to Murder: Diminished Responsibility [1997] NSWLRC 82
Mental Health and Cognitive Impairment Forensic Provisions Bill 2020: Second Reading Speech
Public Defenders Sentencing Table: Manslaughter Substantial Impairment
Cases:
Extracted Legislation:
CRIMES ACT 1900 - SECT 23A Substantial impairment because of mental health impairment or cognitive impairment
Substantial impairment because of mental health impairment or cognitive impairment
(1) A person who would otherwise be guilty of murder is not to be convicted of murder if--
(a) at the time of the acts or omissions causing the death concerned, the person's capacity to understand events, or to judge whether the person's actions were right or wrong, or to control himself or herself, was substantially impaired by a mental health impairment or a cognitive impairment, and
(b) the impairment was so substantial as to warrant liability for murder being reduced to manslaughter.
(2) For the purposes of subsection (1) (b), evidence of an opinion that an impairment was so substantial as to warrant liability for murder being reduced to manslaughter is not admissible.
(3) If a person was intoxicated at the time of the acts or omissions causing the death concerned, and the intoxication was self-induced intoxication (within the meaning of section 428A), the effects of that self-induced intoxication are to be disregarded for the purpose of determining whether the person is not liable to be convicted of murder by virtue of this section.
(4) The onus is on the person accused to prove that he or she is not liable to be convicted of murder by virtue of this section.
(5) A person who but for this section would be liable, whether as principal or accessory, to be convicted of murder is to be convicted of manslaughter instead.
(6) The fact that a person is not liable to be convicted of murder in respect of a death by virtue of this section does not affect the question of whether any other person is liable to be convicted of murder in respect of that death.
(7) If, on the trial of a person for murder, the person contends--
(a) that the person is entitled to be acquitted on the ground that the person was not criminally responsible because of mental health impairment or cognitive impairment, or
(b) that the person is not liable to be convicted of murder by virtue of this section,
evidence may be offered by the prosecution tending to prove the other of those contentions, and the Court may give directions as to the stage of the proceedings at which that evidence may be offered.
(8) For the purposes of this section, a
"person has a cognitive impairment" if--
(a) the person has an ongoing impairment in adaptive functioning, and
(b) the person has an ongoing impairment in comprehension, reason, judgment, learning or memory, and
(c) the impairments result from damage to or dysfunction, developmental delay or deterioration of the person's brain or mind that may arise from a condition set out in subsection (9) or for other reasons.
(9) A cognitive impairment may arise from any of the following conditions but may also arise for other reasons--
(a) intellectual disability,
(b) borderline intellectual functioning,
(c) dementia,
(d) an acquired brain injury,
(e) drug or alcohol related brain damage, including foetal alcohol spectrum disorder,
(f) autism spectrum disorder.
CRIMES ACT 1900 - SECT 4C
Mental health impairment
(1) For the purposes of this Act, a
"person has a mental health impairment" if--
(a) the person has a temporary or ongoing disturbance of thought, mood, volition, perception or memory, and
(b) the disturbance would be regarded as significant for clinical diagnostic purposes, and
(c) the disturbance impairs the emotional wellbeing, judgment or behaviour of the person.
(2) A mental health impairment may arise from any of the following disorders but may also arise for other reasons--
(a) an anxiety disorder,
(b) an affective disorder, including clinical depression and bipolar disorder,
(c) a psychotic disorder,
(d) a substance induced mental disorder that is not temporary.
(3) A person does not have a mental health impairment for the purposes of this Act if the person's impairment is caused solely by--
(a) the temporary effect of ingesting a substance, or
(b) a substance use disorder.
MENTAL HEALTH AND COGNITIVE IMPAIRMENT FORENSIC PROVISIONS ACT 2020 - SECT 4 Mental health impairment
(1) For the purposes of this Act, a
"person has a mental health impairment" if--
(a) the person has a temporary or ongoing disturbance of thought, mood, volition, perception or memory, and
(b) the disturbance would be regarded as significant for clinical diagnostic purposes, and
(c) the disturbance impairs the emotional wellbeing, judgment or behaviour of the person.
(2) A mental health impairment may arise from any of the following disorders but may also arise for other reasons--
(a) an anxiety disorder,
(b) an affective disorder, including clinical depression and bipolar disorder,
(c) a psychotic disorder,
(d) a substance induced mental disorder that is not temporary.
(3) A person does not have a mental health impairment for the purposes of this Act if the person's impairment is caused solely by--
(a) the temporary effect of ingesting a substance, or
(b) a substance use disorder.
MENTAL HEALTH AND COGNITIVE IMPAIRMENT FORENSIC PROVISIONS ACT 2020 - SECT 5
Cognitive impairment
(1) For the purposes of this Act, a
"person has a cognitive impairment" if--
(a) the person has an ongoing impairment in adaptive functioning, and
(b) the person has an ongoing impairment in comprehension, reason, judgment, learning or memory, and
(c) the impairments result from damage to or dysfunction, developmental delay or deterioration of the person's brain or mind that may arise from a condition set out in subsection (2) or for other reasons.
(2) A cognitive impairment may arise from any of the following conditions but may also arise for other reasons--
(a) intellectual disability,
(b) borderline intellectual functioning,
(c) dementia,
(d) an acquired brain injury,
(e) drug or alcohol related brain damage, including foetal alcohol spectrum disorder,
(f) autism spectrum disorder.
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