G. Effect of a Mental Disturbance Short of Insanity on Mens Rea

• Author: Kent Roach
• Profession: Faculty of Law and Centre of Criminology. University of Toronto
• Pages: 301-302

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Evidence of a mental disorder may fall short of establishing a mental disorder defence but may raise a reasonable doubt as to whether the accused had a subjective mental element required for a particular offence. The insanity defence focuses on capacity and has to be proven on a balance of probabilities, whereas the mental element focuses on actual intent and is rebutted by any evidence that raises a reasonable doubt. Thus, it should not be surprising that evidence of mental disturbance, short of establishing a full section 16 defence, could still raise a reasonable doubt about some forms of mens rea.

In R. v. Baltzer,⁸⁵Macdonald J.A. reasoned that in order to determine what was in the accused’s mind, the jury must have evidence of the accused’s "whole personality and background including evidence of any mental illness or disorder that he may have suffered from at the material time." It is an error of law for a judge to instruct the jury to disregard evidence of mental disorder if the defence of insanity fails.⁸⁶All the evidence, including that of mental disorder, should be considered in determining whether the accused had the requisite intent. The higher the degree of mens rea, the more likely it is that mental disorder may raise a reasonable doubt about the particular intent. For example, evidence of mental disorder short of establishing the insanity defence may raise a reasonable doubt as to whether murder was planned and deliberate.⁸⁷Some judges have confused the relevance of evidence of mental disturbance to the determination of mens rea with the separate issue of Parliament’s choice not to create a defence of diminished responsibility to reduce a killing from murder to manslaughter.⁸⁸Although there is no defence of diminished responsibility in Canadian criminal law, the growing consensus is that evidence of mental disturbance or illness

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should be considered when determining whether the accused had the required mens rea. Such evidence may prevent the Crown from proving that the accused had the subjective foresight of death required for a murder conviction. In such a case, an accused could be acquitted of murder but could still be found to have the mens rea necessary for manslaughter. This would occur through ordinary mens rea...