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Investigating Insanity Cases: Part 1

February 10, 2021  By Peter Collins

Actus non facit reum nisi mens sit rea “An act does not make a person guilty of a crime unless that person’s mind be also guilty.” 

The defence of insanity is perhaps one of the least or most poorly understood concepts in criminal law. The reason for this misunderstanding is partly due to the fact that law has borrowed a word from everyday speech and turned it into a legal concept with a very different meaning. In Court, the challenge is to ensure that this common concept of insanity does not invade the legal concept.

About 25 years ago, crown attorney James Cornish and I wrote a paper for homicide detectives on how to investigate cases to determine the issue of criminal responsibility.  Although distributed on a case by case basis, we never published it. In honour of James, who recently retired, I am now sharing an updated version.

Part 1 will address the legal definition, the myths and realities of the Not Criminally Responsible on Account of Mental Disorder (NCRMD) and what to investigators should evaluate at the crime scene.


It is beyond the scope of this article to examine the development and case law regarding s. 16 of the Criminal Code of Canada: Insanity is presumed not to be present and must be demonstrated to exist on a balance of probabilities, by whichever party is asserting the defence. According to section 16 of the Criminal Code of Canada, there is a prerequisite that the accused suffers from a mental disorder that affects the accused to a degree that causes the accused to lack appreciation for the nature and quality of the act committed and/or to lack knowledge or understanding of its moral and/or to lack legal wrongfulness.[2]

Myths and Realities[3]

  • The insanity defence is overused: The insanity defence is raised less than 1 per cent of criminal prosecutions in Canada and is only successful in 10 per cent of cases in which it is raised.
  • Many accused are released from custody soon after being found not criminally responsible: It is very rare for an individual, who is been found NCRMD, to be released immediately after the finding.
  • NCRMD accused spend less time in custody than would have been the case if they had been convicted of the offense and serve the sentence for it: The contrary is true. Those found not criminally responsible often spend considerably more time under the auspices of the provincial review board responsible for overseeing individuals who are NCRMD.
  • A NCRMD verdict is a positive outcome for the accused, and as such, is often raised by the defence: In reality approximately 50 per cent of ‘not criminally responsible’ defences are raised by the Crown.
  • Outcomes of the insanity defence are a result of who is more persuasive in the “battle of experts”: The “battle of the experts” is still uncommon but in my professional opinion appears to be on the increase. A recent example was the attempt of the defence to have autism spectrum disorder, a mental condition that could qualify as a “disease of the mind” that is required for an insanity plea. This is also true in cases when psychiatrists offer the opinion that individuals with PTSD can dissociate and therefore not be responsible for their

The conditions more commonly found in the background to an NCR case include: schizophrenia, delusional disorder, major depressive disorder with psychotic features and mania in the context of a bipolar disorder. It is important to note that the vast majority of individuals who meet the criteria for these diagnoses and end up committing crimes are still responsible for their actions and are not candidates for a section 16 defence.

The more bizarre or atrocious the offence or offences are, the more intuitively satisfying it will be to conclude that the offender was “crazy”. This is where, despite the law in this area, the temptation will be to find the offender insane. It is important that the investigation be thorough, and the more the assistance of an investigative support unit (i.e. the Criminal Behaviour Analysis Section of the Ontario Provincial Police or the Behavioural Sciences Sections of the Royal Canadian Mounted Police and Sûreté du Québec) can help. The behavioural experts can assist in bizarre and shocking crimes by giving focus to the investigators, identifying areas that may be important yet not obvious and providing interview strategies. In a number of cases, the author has been contacted by the police to determine whether the subject is psychologically fit to be interviewed.

Part 2 will explore the investigatory aspects of these cases: crime scene considerations; interviewing the suspect; witness interviews; background investigation and information that should be obtained when the accused is in custody.


[1] Sir Edward Coke, Beverley’s Case (1603), 4 Co. Rep. 123, 117 E.R. 1118.

[1] Bloom, H. (2013) Not Criminally Responsible on Account of Mental Disorder (NCRMD). Law and Mental Disorder: a comprehensive and practical approach. Eds. H. Bloom & R. Schneider. Toronto: Irwin Law.

[1] Adapted from Perlin (1993) The jurisprudence of the insanity defense. Durham, North Carolina: Academic Press

Peter Collins is the operational forensic psychiatrist with the Ontario Provincial Police’s Criminal Behaviour Analysis Section. He is also a member of the crisis/hostage negotiation team of the Toronto Police Service Emergency Task Force. Dr. Collins’ opinions are his own. Contact him at 

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