Homicide and mental illness in New Zealand, 1970–2000

TLDR

Homicides by mentally ill persons have raised political concerns about deinstitutionalisation. The study aims to provide accurate information on the contribution of mental illness to homicide rates. The authors performed a retrospective analysis of 1,498 New Zealand homicides from 1970–2000 using government data, defined mentally abnormal perpetrators as those found unfit to stand trial, not guilty by reason of insanity, convicted and sentenced to psychiatric committal, or convicted of infanticide, and examined group and time trends. Mentally abnormal homicides comprised 8.7 % of all homicides, with a stable annual rate of 1.3 per million; overall homicide rates rose 6 % per year until 1990 then fell, while the proportion of homicides committed by mentally abnormal individuals dropped from 19.5 % in 1970 to 5.0 % in 2000; only 10 % of perpetrators had recent hospital admission and 28.6 % had no prior mental‑health contact, and 74 % of victims were.

Abstract

Homicides by mentally ill persons have led to political concerns about deinstitutionalisation.To provide accurate information about the contribution of mental illness to homicide rates.Retrospective study of homicide in New Zealand from 1970 to 2000, using data from government sources. 'Mentally abnormal homicide'perpetrators were defined as those found unfitto stand trial, not guilty by reason of insanity, convicted and sentenced to psychiatric committal, or convicted of infanticide. Group and time trends were analysed.Mentally abnormal homicides constituted 8.7% of the 1498 homicides. The annual rate of such homicides was 1.3 per million population, static over the period. Total homicides increased by over 6% per year from 1970 to 1990, then declined from 1990 to 2000. The percentage of all homicides committed by the mentally abnormal group fell from 19.5% in 1970 to 5.0% in 2000. Ten percent of perpetrators had been admitted to hospital during the month before the offence; 28.6% had had no prior contact with mental health services. Victims were most commonly known to the perpetrator (74%).Deinstitutionalisation appears not to be associated with an increased risk of homicide by people who are mentally ill.