Criminal law (2022): Justification + Mistake of law + Mistake of fact

Justification is a defense in a criminal case, by which a defendant who committed the acts asserts that because what they did meets certain legal standards, they are not criminally culpable for the acts which would otherwise be criminal. Justification and excuse are related but different defenses (see Justification and excuse).

Justification is an exception to the prohibition of committing certain offenses. Justification can be a defense in a prosecution for a criminal offense. When an act is justified, a person is not criminally liable even though their act would otherwise constitute an offense. For example, to intentionally commit a homicide would be considered murder. However, it is not considered a crime if committed in self-defense. In addition to self-defense, the other justification defenses are defense of others, defense of property, and necessity.

A justification is not the same as an excuse. In contrast, an excuse is a defense that recognizes a crime was committed, but that for the defendant, although committing a socially undesirable crime, conviction and punishment would be morally inappropriate because of an extenuating personal inadequacy, such as mental defect, lack of mental capacity, sufficient age, intense fear of death, lacking the ability to control their own conduct, etc.

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Mistake (criminal law).

A mistake of fact may sometimes mean that, while a person has committed the physical element of an offense, because they were laboring under a mistake of fact, they never formed the mental element. This is unlike a mistake of law, which is not usually a defense; law enforcement may or may not take for granted that individuals know what the law is.

Discussion.

Most criminal law systems in developed states exclude mistake of law as a defense, because allowing defendants to invoke their own ignorance of the law would breach the public policy represented by the Latin maxim: ignorantia legis neminem excusat. But someone operating under a mistake of fact will not generally be liable, because, although the defendant has committed the actus reus of the offense, the defendant may honestly believe in a set of facts that would prevent him or her from forming the requisite mens rea required to constitute the crime.

For example: A defendant goes into a supermarket and places eight items in a basket which is presented to the cashier for payment in the usual way. Both honestly believe that all eight items have been scanned, and the defendant pays the sum shown on the bill. A store detective, however, notices that a mistake was made by the cashier so that only seven items were priced. This detective arrests the defendant after leaving the store. Since the defendant honestly believes that he has become the owner of goods in a sale transaction, he cannot form the mens rea for theft (which is usually dishonesty) when he physically removes them from the store.

There is a complex question as to whether the defense of 'mistake' applies to crimes that do not specify a mental element – such as strict liability offenses and manslaughter by criminal negligence. In Australia, the High Court's 2005 ruling in R v Lavender prevents the use of any 'reasonable mistake of fact' defense in cases of involuntary manslaughter. However, the defense of mistake is available to offenses of strict liability such as drunk driving: see DPP v Bone (2005). And it is the very availability of the defense of 'mistake' that distinguishes between offenses of strict and absolute liability. Mistake of fact is unavailable in respect to absolute liability offenses.

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