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Understanding when weapon use is most likely to occur can support safer and more effective risk assessment and prevention in forensic mental health settings, strengthening community management and developing interventions in forensic psychiatric settings.
A study published in Injury Epidemiology by Dr. Mark Mohan Kaggwa and colleagues examined how often weapons were used during the index offence — the offence that led to the patient’s involvement in the forensic mental health system. The researchers reviewed 819 Ontario Review Board reports from 2014 to 2015 and assessed the characteristics of the patients (for example, age, gender, psychiatric diagnosis, hospitalization history) and of the people they assaulted with a weapon (including relationship to the patient, age, gender) to identify which factors were associated with weapon use during the index offence.
This is a plain language summary of:
Kaggwa, M. M., Davids, A., Mohibi, P., Erb, B., Bradford, J., Chaimowitz, G. A., & Olagunju, A. T. (2024). Weapon use during the index offense: A study among forensic psychiatry patients in Ontario, Canada. Injury epidemiology, 11(1), 66. https://doi.org/10.1186/s40621-024-00551-z
Key Findings
In this study, 48 per cent of patients used a weapon during their index offence. Most were men, with an average age of 34 years. Most people who were assaulted were men as well.
The researchers found that a history of psychiatric hospitalization was the only significant patient factor. Patients who had been hospitalized before their index offence were 57 per cent less likely to use a weapon. Being diagnosed with a personality disorder was not a significant factor after adjusting for other variables.
People who were assaulted who were also extended family members were among those most likely to be attacked with a weapon; followed by siblings; lovers, partners, and spouses; parents; and adult acquaintances. Adult strangers were the least likely. However, compared with adult strangers, people who were assaulted who were also female, health-care workers, or law-enforcement professionals were even less likely to be attacked with a weapon during the index offence.
Why It Matters for Care and Policy
Because previous psychiatric hospitalization was linked to lower odds of weapon use during the index offence, the authors suggest that earlier contact with the mental health system may help reduce the risk of later weapon-related violence. They suggest that access to psychiatric care, maintenance treatment, continuous support and monitoring, and follow-up are key components of risk management.
The study highlights that victim–patient relationships strongly influenced the likelihood of weapon use, emphasizing the need for mental health professionals to consider family and relational contexts when planning community management and monitoring.
The authors also identify a need for policies, action plans, and interventions that are informed by current evidence on the factors linked to weapon use among forensic mental health patients.
Looking Ahead
The authors noted that some information — such as the specific weapons used — was not available in the Ontario Review Board reports, which limited how precisely they could examine the links between the weapon used and the characteristics of the patient and the people they assaulted.
They added that additional clinical and contextual data would help clarify why weapons are used in some index offences but not others.
Written by Kyle Roerick and approved by Dr. Mark Mohan Kaggwa
