The community perception that the mentally ill are dangerous contributes to the stigma experienced by those with schizophrenia,1,2
and the risk of homicide by the mentally ill has been used as an argument against deinstitutionalization.3
Publicity arising from homicides of complete strangers by psychotic individuals appears to have been a catalyst for changes in mental health policy and for laws governing compulsory psychiatric treatment.4,5
In Canada, the killing of Brian Smith, a former professional ice hockey player and sports broadcaster, by a mentally ill patient led to an amendment to the Mental Health Act and the Health Care Consent Act that became known as “Brian's Law.”6
The law introduced community treatment orders and new criteria for involuntary commitment to psychiatric facilities. Similar changes were introduced in New York after the killing of a young woman, Kendra Webdale, by a recently discharged psychotic patient.7
In the United Kingdom, the Clunis enquiry into the killing of Jonathan Zito at a London railway station recommended that every patient about to be discharged from a psychiatric hospital be subjected to a formal risk assessment.8
Health and policy measures that aim to protect the public from violence by the mentally ill might be justified if the threat of violence was greater than that of the nonmentally ill. There is a modest but consistent association between mental illness and serious violence,9
However, measures aimed at the care and control of current patients would have a limited effect on the number of stranger homicides if many of these events occur during the first episode of psychosis, after the emergence of psychotic symptoms, but before diagnosis and treatment. Recent studies, including a systematic review and meta-analysis, show that the rate of homicide during first-episode psychosis is as much as 15 times greater than the annual rate after treatment.11,12
These studies also suggest that the rate of homicide committed by previously treated psychotic patients is lower than the widely accepted estimate of 1 in 3000 schizophrenic males per year. 13
The same might be true for rates of stranger homicide, although few studies have considered the association between serious mental illness and stranger homicide, or the phase of mental illness in which a stranger homicide is more likely to occur. If a significant proportion of those who kill strangers in the course of psychotic illness have never received treatment with antipsychotic medication, then measures to reduce the risk of future harm by known patients can have a limited effect, and measures that improve early detection and treatment of psychosis might be a more successful way to reduce the incidence of stranger homicide.
Studies that have reported the relationship between mentally ill homicide offenders and their victims show that the proportion of victims who are strangers is low.11,14,15
A study of stranger homicide in England and Wales over a 3-year period from 1996 to 1999 found that people with a diagnosis of schizophrenia were responsible for 7.8% of all homicides and 4.3% of the stranger homicides.16
Although stranger homicides increased in England and Wales between 1967 and 1997, the increase was mainly due to lethal assaults by young men intoxicated with alcohol.
A study of stranger homicide in Canada reported that 1.7% of stranger homicide offenders were mentally retarded or mentally ill. None were found to have a clearly psychotic motive for the homicide, but about one-quarter of the patients were reported to have paranoia or a sense of “impending doom.”17
The authors concluded that those who killed strangers were similar in most respects to those who killed acquaintances.
One of the few studies reporting the characteristics of a group of mentally ill offenders who attempted to kill strangers described 20 people who had pushed subway passengers in front of oncoming trains.18
Three were charged with murder. The offenders had a mean age in the mid-30s, three-quarters were men and two-thirds were homeless. Nineteen of the 20 offenders had an established diagnosis of schizophrenia and all but one of those where thought to have positive symptoms of psychotic illness at the time of the offence.
In the first part of the study, we aimed to estimate, using a meta-analysis of published data, the proportion of homicides committed during psychotic illness in which the victim was a stranger and the incidence of stranger homicide. In the second part of the study, we examined a separate sample of homicide offenders with psychosis who had killed strangers, with particular reference to the proportion of those offenders who had previously received treatment with antipsychotic medication. Finally, we aimed to compare the characteristics of stranger homicide offenders with psychosis with a case–control group who killed a family member.