Criminal Law: “Mistake of Law” v. “Mistake of Fact” Defense

Mistake of Law

Mistake of Law is rarely a justifiable pre-trial defense. The Mistake of Law” is when a person knows they committed an act, but they did not know the conduct was against the law. It is different between “Mistake of Fact”. There are few circumstances where “Mistake of Law” is a justifiable defense. Arizona does not accept except ignorance, or lack of knowledge that a particular law exists as a valid defense. This is described under Arizona Law A.R.S. §13-204 (B). Not being aware or having knowledge of the law does not relieve a person of criminal liability. Mistake or lack of knowledge of the law itself, is not itself a justifiable defense

Mistake of Fact

Mistake of Fact occurs when a person is not conscious of the facts that existed material to the offense. An Example of “Mistake of Fact”: A person buys a vehicle from a private owner. He is later arrested for purchasing a stolen vehicle. That’s when he learns the seller stole the vehicle to begin with. The buyer mistakenly believed that the seller was the valid owner of the vehicle. This is a justifiable defense.

Unfortunately, there are many circumstances that occur where a person is not aware of a DUI or criminal law because they are new to Arizona or visiting from a different state. For example, they may be arrested for DUI “impaired to the slightest degree”, with a BAC below the .08% legal limit. A person charged with being “impaired to the slightest degree” means they are accused of driving under the influence of alcohol under the Blood Alcohol Content legal limit of .08% or Drugs.

It is not a justifiable defense for the defendant to argue that they were not aware that they could be charged with DUI if they were driving under the influence of drugs or alcohol under the .08% legal limit.