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Is sleepwalking a legitimate criminal defence?

Sleepwalkers can perform surprisingly complex tasks while unconscious, including cooking and driving. It has sometimes, however, also included violent crime that leads to a rare and difficult-to-prove defence.

Canada has seen at least two acquittals on a sleepwalking defence, and many more sleepwalking cases have emerged in the United States and United Kingdom, although most of them resulted in convictions.

Legally, such a defence is called automatism. It acknowledges the guilty act, but denies the perpetrator was aware of their actions, so they lacked guilty intentions, and are therefore not criminally responsible.

It’s not the same as criminal insanity though, as the Supreme Court of Canada noted in a landmark 1992 decision.

The case dated from 1987 when an Ontario man drove 23 kilometres to his in-laws’s home, killing his mother-in-law and injuring her husband. He then drove to a police station and turned himself in, saying “I think I may have killed some people.” He claimed no memory of what he’d just done.

Sleepwalking might seem like a convenient excuse for the crime, but multiple factors dovetailed to support his story.

  • Medical tests and experts found evidence of parasomnia, a realm of sleep disorders that include sleepwalking.
  • He was under severe stress due to gambling debts and loss of his job.
  • There was no motive since he was on good terms with his in-laws.
  • He was unaware of his own injuries, severed tendons in both hands.

In 2000, another Ontario man was acquitted of attempted murder after trying to cut his girlfriend’s throat while she slept. A psychiatrist diagnosed him as a parasomniac and he was found not criminally responsible. However, that same man attempted to kill again in 2014 — this time while awake — and committed suicide after his victim escaped.  That, however, doesn’t mean the 2000 verdict was necessarily wrong, or the result of a misdiagnosis.

In other cases outside Canada, judges and juries rejected automatism in cases where the crime showed too high a level of organization or complexity for an unconscious person, or where a previous motive existed. Also, certain difficult-to-fake medical tests can indicate parasomnia, making it difficult for a faker to get away with it.

Read more:

Defences in Canadian Criminal Law

Defence of Automatism