Crimes Act 1900

A person on trial for murder shall not be convicted of murder if, when the act or omission causing death occurred, the accused was suffering from an abnormality of mind (whether arising from a condition of arrested or retarded development of mind or any inherent cause or whether it was induced by disease or injury) that substantially impaired his or her mental responsibility for the act or omission.

An accused has the onus of proving that he or she is, under subsection (1), not liable to be convicted of murder.

A person who, apart from subsection (1), would be liable (whether as principal or accessory) to be convicted of murder is liable to be convicted of manslaughter.

The fact that a person is, under subsection (1), not liable to be convicted of murder does not affect the question whether any other person is liable to be convicted of murder in respect of the same death.

If, on a trial for murder, the accused contends—

that he or she is entitled to be acquitted on the ground that he or she was mentally ill at the time of the act or omission causing the death; or

that he or she is, under subsection (1), not liable to be convicted of murder;