Schizophrenia disorders, substance abuse and prior offending in a sequential series of 435 homicides

Objective: To examine the relationship between committing homicide, the presence of schizophrenia, substance misuse and past criminality. Method: The study employed a data linkage design, using contacts recorded on two statewide databases, one of which recorded public mental health services contacts and the second of which recorded contacts with the police. The estimated rates of schizophrenia disorders, substance abuse and criminal convictions found among a population of 435 homicide offenders were contrasted with estimated rates in two composite comparison samples. Results: Of the 435 offenders, 38 (8.7%) had been diagnosed with a schizophrenia disorder, which was RR 13.11 (95% CI 9.14-18.80) times more likely than a comparison sample. Rates of known substance abuse between homicide offenders with and without schizophrenia and community-dwelling residents with schizophrenia did not differ significantly. However, these rates were higher than those found in the general community. A similar pattern emerged for comparisons regarding offending histories between these same groups. Conclusion: The association between homicidal violence and having a schizophrenia disorder cannot be explained away simply on the basis of either comorbid substance abuse or prior criminal offending