Rates of homicide and homicide associated with severe mental illness in NSW between 1993 and 2016

Abstract

Objective: To describe the characteristics of offenders found not guilty on the grounds of mental illness (NGMI) in New South Wales and rates of NGMI and other homicide verdicts. Method: Demographic, legal and clinical data after referral to the NSW Mental Health Review Tribunal following an NGMI verdict for homicide matched with results from the National Homicide Monitoring Program. Results: Between 1993 and 2016, a total of 2159 homicide offenders were dealt with by the NSW courts, including 169 (7.8%) who were found NGMI. Over this period, the rate of non-NGMI homicide convictions fell from 1.83 per 100,000 per annum to 0.65 per 100,000 per annum (Kendall’s tau = −0.79, p ⩽ 0.001) while the rate of NGMI homicide fluctuated, with an average annual rate of about 0.1 per 100,000 per annum (Kendall’s tau = 0.17, p = 0.23). There was no association between the annual rates of NGMI and non-NGMI homicides (Pearson r = −0.3, p = 0.16) but falling rate of non-NGMI homicide meant that the proportion of NGMI offences doubled from 5.5% in the first 12 years to 11% in the second 12 years. Nearly all (88.7%) of those found NGMI had a schizophrenia-related psychosis. However, there were high rates of psychiatric comorbidity including substance use disorder (60.7%) and a history of a prior head injury (41.1%). Most (83.4%) of the NGMI offenders had previous contact with mental health services, but only half of these had received treatment with antipsychotic medication. Conclusion: The fall in conviction for homicide offences in the last 24 years has not been matched by a reduction in NGMI homicide verdicts. More assertive treatment of emerging psychosis and comorbid substance use disorders, and improved continuity of care of chronic psychosis might prevent some homicides.

Homicide in the context of psychosis: analysis of prior service utilisation and age at onset of illness and violence

“…This has also not materialised. 36 , 37 At present, population-based data are required to better link the effects of these early and more assertive community interventions to homicide rates among those with SMI. Systems- and other macro-level variables (e.g.…”

Homicide associated with psychotic illness: What global temporal trends tell us about the association between mental illness and violence

“…(c) Penney et al (2018) and Nielssen et al (2021) observed falling TPH rates during their time series but PRH rates did not change.…”

“…In order to distinguish between these divergent observations, there are now eight well-designed longitudinal studies that can help to better understand these dynamics, notably Nielssen et al (2021) in this journal and the recently published Golenkov et al (2021). In contrast to cross-sectional studies, longitudinal investigations permit an analysis of homicide rates over time and thus can more sensitively examine the nature of the association between TPH and PRH.…”

“…Similarly, expected declines in PRH rates resulting from better community care and first-episode services in the post de-institutionalization era have also not materialized (e.g. Flynn et al, 2021; Nielssen et al, 2021).…”

“…(a)Sturup and Lindqvist (2014) andFlynn et al (2021) are both studies where TPH was relatively stable and there was little change in PRH rates; (b)Taylor and Gunn (1999),Simpson et al (2004) andLarge et al (2008) each describe the trend where rates of TPH rose while PRH rates were static; (c)Penney et al (2018) andNielssen et al (2021) observed falling TPH rates during their time series but PRH rates did not change.…”