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Tanaka Criminal Law Casebook

Mistake of Fact or Law

Sometimes, a mistaken belief may prevent a defendant from being criminally culpable where he/she/they would otherwise be guilty of a crime.  It is important to determine whether a mistake should be classified as a mistake of fact or a mistake of law.

More frequently, a mistake of fact may serve as a defense - where a defendant is mistaken as to the ownership of property (larceny), mistaken as to the presence of a person in a building set for demolition (assault/murder), etc.  Rarely, a mistake of law will provide a basis for a defense.