R. v. Mohan

R. v. Mohan 2 S.C.R. 9 is a leading Supreme Court of Canada decision on the use of experts in trial testimony.

Background

Dr. Chikmaglur Mohan was a pediatrician in North Bay, Ontario. He was charged with sexual assault of four teenaged patients. During his trial, the defence tried to put Dr. Hill, a psychiatrist, on the stand as an expert on sexual assault. Hill was intended to testify that the culprit of the offence must have possessed several abnormal characteristics of which Mohan did not have. In a voir dire, Hill testified that the culprit of the first three assaults was likely a pedophile, while the fourth would have been by a sexual psychopath. This evidence was held to be inadmissible by the judge. Mohan was eventually convicted at trial but was overturned on appeal.

The issue before the Supreme Court was whether Hill's testimony could be admitted as an expert witness, and whether the testimony would violate the rule against character evidence.

Opinion of the Court

Justice Sopinka, for a unanimous Court, allowed the appeal and held that the evidence should be excluded.

Expert evidence, stated Sopinka, should be admitted based on four criteria. It must be relevant, necessary to assist the trier of fact, should not trigger any exclusionary rules, and must be given by a properly qualified expert.

Relevance is a question of law and so is determined by the judge. Where it approaches the "ultimate issue" of the trial the standard for inclusion must be...
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