The methodology and impact of independent inquiries of homicides by people in care of mental health services have been questioned.

To analyse characteristics of patients who committed homicide, their victims and inquiries published in England between 2010 and 2023.

Documentary and thematic analysis of 162 mental health homicide inquiries. We compared characteristics of perpetrators with those from the National Confidential Inquiry into Suicide and Safety (2018), and characteristics of victims with those in the general population of England and Wales. We examined methodology used by inquiries and thematically analysed root causes, contributory factors, recommendations, action plans, predictability and preventability.

Fifty-two per cent of perpetrators had a diagnosis of schizophrenia and 52% had a history of non-adherence to medication and follow-up; 71% of victims in mental health homicides were family, friends or partners compared with 44% in the general population; 77% of inquiries used no clear methodology. The most frequent root causes and contributory factors related to deficits in assessment, treatment, follow-up or discharge, and risk assessment. There was no direct link between putative causes and resulting recommendations. The most frequent recommendations related to changing policy, improving clinical governance and training. Only 4% of inquiries deemed the homcide to be predictable and preventable.

There is considerable variation in the methodology of mental health homicide inquiries, with little use of human factors and systems theory. Inquiries repeatedly identify the same themes, and most mental health homicides are found to be neither predictable nor preventable. We make recommendations for improving consistency and usefulness.