Sentencing Trends No 8 — From Murder to Manslaughter: Partial defences in New South Wales — 1990 to 1993

Hugh Donnelly
Research Officer

Stephen Cumines
Principal Research Officer


The partial defence of diminished responsibility was introduced in NSW in 1974, modelled on s 2 of the English Homicide Act 1957. The defence is defined under s 23A of the Crimes Act 1900 (NSW), as follows:

23A(1) Where, on the trial of a person for murder, it appears that at the time of the acts or omissions causing the death charged the person was suffering from such abnormality of mind (whether arising from a condition of arrested or retarded development of mind or any inherent causes or induced by disease or injury) as substantially impaired his mental responsibility for the acts or omissions, he shall not be convicted of murder.

The remaining sub-sections of s 23A state that once the defence is established the accused is liable to be convicted of manslaughter and provides that evidence may be offered by the Crown tending to disprove the defence (s 23A(5)).

The defence must be proved by the defendant on the balance of probabilities (see Tumanako (1992) 64 A Crim R 149 at p 159 per Badgery-Parker J) The jury has a duty to consider medical evidence and cannot reject unanimous medical evidence in die absence of other evidence displacing it or throwing doubt upon it (Taylor (1978) 22 ALR 599). A number of conditions have been recognised as amounting to an abnormality of mind including schizophrenia, epilepsy, depression (reactive and endogenous) personality disorders and psychopathy (see NSW Law Reform Commission Discussion Paper No 31 at p 82).