An investigation of 435 sequential homicides in Victoria : the implication of psychosis, motive for offending, substance abuse and gender
thesisposted on 16.01.2017 by Bennett, Debra Jane
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Homicide, and the characteristics of those who perpetrate it, has long been of interest to researchers and, indeed, the general public. Any differences in the characteristics of female homicide offenders in particular have largely been ignored. However, many examinations of the relationship between mental illness and serious violence, substance abuse, criminality and motivation have been encumbered by methodological limitations. This research aimed to overcome some of the methodological limitations that have characterized much of the previous literature and gain a more comprehensive clarification regarding differences between genders, differences in the impact of co-morbid substance abuse, number of mental health contacts, prior offending and differences in motivation and victim selection for homicide offenders who have a psychotic illness and those who do not. These data linkage studies utilized an entire population of homicide offenders from 1997-2005 (N=435) in Victoria, Australia. Murder-suicide offenders were also included. Police data were linked to a state wide register of public mental health contacts and rates of mental health diagnoses (particularly psychosis), prior mental health contacts, known substance abuse, criminal convictions and other index offence characteristics such as motive and victim selection were established. Identical methodology was used to compare rates of psychotic illness, substance abuse and prior offending in two randomly selected community samples. Substance abuse and prior offending were also compared with a non-offending schizophrenia group. Of the homicide offenders in total, 38 (8.7%) were diagnosed with schizophrenia and 24 (5.5%) were diagnosed with affective disorders; they were 13.4 times more likely than comparisons to have schizophrenia and female offenders (n=55) were 43 times more likely than their comparison group. Only one woman killed during the first episode of psychosis; those female offenders diagnosed with a psychotic illness had received their diagnosis on average 7.15 years previous to the offence; a relatively long prior history of mental illness. Of the male offenders (n=380), 43.3% of those with diagnosed schizophrenia (n=30) committed their offence during first episode. Of the entire sample, 117 (26.9%) had some prior mental health contact. Although homicide offenders’ rate of known substance abuse was higher than in the general community, and among schizophrenia comparisons after cases with a criminal history were excluded, there was no difference between those offenders with schizophrenia and other homicide offenders or those with schizophrenia in the community. A similar pattern emerged in the comparison of prior offending history between those with and without schizophrenia and their relative comparison groups. Homicide offenders with schizophrenia had higher rates of prior offending than the general community comparisons and those comparisons that had schizophrenia but had not committed homicide. Homicide offenders with schizophrenia were less likely to kill a stranger but were 2.17 times more likely to kill a relative and 2.6 times more likely to be motivated by revenge than those without schizophrenia.