Judgments of predictability, preventability and causation of mental health homicides in England 2010 - 2023.

Independent mental health homicide inquiries in England are required to comment on predictability and preventability and attribute causation. National commissioning bodies do not provide definitions. This study examines how predictability and preventability were determined, and causality attributed, by independent mental health homicide inquiries published in England between 2010 and 2023. The conceptual underpinnings of predictability and preventability in other specialities of medicine, and in suicide and homicide assessments in psychiatry are examined. We found 189 independent reports relating to mental health homicides, of which 162 independent homicide inquiries were included in the final analysis. No inquiry described how it attributed causation or addressed cognitive biases. A total of 130 of the 162 inquiries (80%) commented on either predictability or preventability: of these, only eight (6%) included a clear definition of predictability and preventability. Homicides were deemed predictable if the inquiry panel felt that the perpetrator's words or actions should have alerted professionals to a risk of significant violence; and preventable if the clinical team had knowledge, legal means, and opportunity to stop the homicide from occurring. 105 inquiries (81%) provided a firm view on both predictability and preventability. Of these, four homicides (4%) were deemed to be both predictable and preventable, ten (9%) were preventable but not predictable, five (5%) were predictable but not preventable, and 86 (82%) were neither predictable nor preventable. The implications of these findings are discussed, with recommendations to national commissioning bodies.