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Lavallee and her common law partner Rust (the victim) had an abusive relationship, however she kept coming back. On the night of the killing, there was a party at their house. Rust hit her and told her that she was going to "get it" when all the guests left. He threatened to harm her, saying "either you kill me or I'll get you". During the altercation Rust slapped her, pushed her and hit her twice on the head. At some point during the altercation he handed Lavallee a gun, which she first fired through a screen. Lavallee contemplated shooting herself, however when Rust turned around to leave the room she shot him in the back of the head. She was charged with murder. A psychiatrist gave expert evidence at trial describing her state of mind, and that she felt as though she was "trapped" and that she would have been killed if she did not kill him. The jury acquitted her at trial, but this was overturned at the Court of Appeal who ordered a new trial. Lavallee appealed this order to the Supreme Court.


  1. Can expert evidence be used in a claim of self-defense, and if so, to what extent?


Appeal allowed, acquittal restored.


The jury's acquittal seems to have heavily relied upon Dr. Shane's (the psychiatrist's) assessment of the appellant and his testimony. He stated that she felt as though she was trapped, and that she felt as if she would be killed if she did not act first. However, the appeal court stated that this evidence was not admissible because it swayed the jury and did not elaborate on the facts but merely provided an opinion.

Wilson, writing for a unanimous court, vehemently disagrees. After going into the history of spousal abuse and the effects that it has on the women who are abused, she held that expert evidence is very much admissible and helpful in establishing the necessary elements were present for s.34(2) to provide a defence. This section requires the accused to have reasonably believed that she was in danger, and that she had no other option to stop it other than causing death or grievous harm. As?

The Court holds that expert evidence is very helpful in determining how a reasonable person would have acted in the situation. It allows the jury to understand the situation that the woman was in and what she was thinking. In this case, it helps them realize that despite the fact that she shot him while he was walking away, she still thought that her life was in serious danger. She believed that he was going to kill her later on that night if she did not act first. This expert testimony helps prove that the defence was not too far removed temporally, or too violent to have been reasonable in the circumstances. Therefore, the trial judge did not err in allowing Dr. Shane's testimony to be used as evidence available to the jury.


  • Self-defence applies even when you are not directly or immediately in harm.
  • Expert testimony can be very helpful in claims of self-defence as it helps the jury/judge understand the condition that the accused was in when they acted and allows for an objective determination if their actions were reasonable in the circumstances.
  • Actions that claim to be in self-defence but are too temporally removed or violent in the circumstances to be considered reasonable will not satisfy the s.34(2) requirements to be a defence.