Systematic review of stranger homicides by psychotic individuals

Abstract

Background and hypothesis: Individuals with psychosis have an increased risk of committing and being victims of violence. There are frequent media reports of psychotic individuals assaulting strangers, which may cause fear and stigmatization among the general public. We hypothesize that homicides targeting strangers by psychotic individuals are rare.

Study design: Systematic review and meta-analysis to assess what percentage of homicide offenders suffering from psychosis target strangers. Medline database was searched with search term 'psychosis OR schizophrenia AND homicide' from inception to 10/2024. Articles published in peer-reviewed journals, written in English, and reporting the total number of homicide offenders with psychosis (ICD-10: F20, F22, F25, F30-F31, F32.3, F29) and stranger victims were included. PRISMA guidelines were followed. Studies with inadequate data were excluded. A random-effects meta-analysis using meta and metafor packages in R version 4.4.2 was conducted using the restricted maximum-likelihood (REML) method to account for variability across studies. The primary outcome was the pooled rate of stranger homicides among individuals with psychosis who committed a homicide, expressed as a proportion with 95% confidence intervals (CIs).

Study results: Thirteen studies were included, comprising a total of 1,438 perpetrators who had killed 177 strangers. Meta-analysis of these studies indicates that 12.7% (95% CI: 7.85-17.56 and heterogeneity I2 89.49%) of the homicides by psychotic individuals are targeted at strangers. Male gender explained 26.9% of between-study variance (P-value<0.05).

Conclusions: Although still rare, the percentage of homicides committed by psychotic individuals and targeted at strangers is higher than previously reported.

Keywords: psychosis; schizophrenia; violence.