Lavallee v. Her Majesty the Queen

The appellant, a battered woman, killed her abusive partner after an argument in which he threatened her life. In her defense, the appellant offered the expert testimony of a psychiatrist who testified regarding battered woman syndrome. The appellant was ultimately acquitted. The Manitoba Court of Appeal overturned the acquittal, and the Supreme Court of Canada considered whether the expert testimony of the psychiatrist should have come before the court and whether the judge’s instructions on said testimony were appropriate. The Supreme Court held that the testimony was admissible “where the expert has relevant knowledge or experience beyond that of the lay person,” as in the case of battered woman syndrome, and where the testimony is relevant to understanding the “reasonableness” of the defendant’s perspective.