Criminal Code Act 1899

When a person who unlawfully kills another under circumstances which, but for the provisions of this section, would constitute murder, is at the time of doing the act or making the omission which causes death in such a state of abnormality of mind (whether arising from a condition of arrested or retarded development of mind or inherent causes or induced by disease or injury) as substantially to impair the person’s capacity to understand what the person is doing, or the person’s capacity to control the person’s actions, or the person’s capacity to know that the person ought not to do the act or make the omission, the person is guilty of manslaughter only.

On a charge of murder, it shall be for the defence to prove that the person charged is by virtue of this section liable to be convicted of manslaughter only.

When 2 or more persons unlawfully kill another, the fact that 1 of such persons is by virtue of this section guilty of manslaughter only shall not affect the question whether the unlawful killing amounted to murder in the case of any other such person or persons. sch 1 pt 5 ch 28 s 304A ins 1961 10 Eliz 2 No. 11 s 5