Criminal Defenses

Actus Reus Defenses

It is a defense to any criminal charge that the defendant did not commit the criminal act, and in every case the prosecution has the burden of proving the actus reus. The prosecution also has the burden of proving that the defendant's criminal act was voluntary. However, since criminal law assumes free will, few acts will ever be considered involuntary. Among the rare acts the criminal law considers involuntary are those committed as a result of a reflex or seizure, or while the defendant was in an unconscious state. For example, a defendant who commits a criminal act while sleepwalking or in a state of shock secondary to serious bodily injury might have a defense of “automatism,” since the act might be considered involuntary. As a practical matter, however, this defense is rarely raised or successful.

Mens Rea Defenses

A much broader category of criminal defenses relates to mens rea. Many criminal statutes require proof of a specific mental state, such as intent, depraved indifference, recklessness, or negligence. Here too the prosecution bears the burden of proof. Thus, where a crime is defined to include a particular state of mind, and the prosecution fails to prove that the defendant acted with that particular mental state, the defendant must be acquitted, or convicted of charge conforming to the form of mens rea that is proven. To put it another way, lack of the requisite mens rea is always a defense to a criminal charge. For example, if a defendant is charged with intentional murder, and the prosecution is able to prove only recklessness (i.e., that the defendant did not intend to kill, but knew that he or she was placing the victim's life at risk), the defendant is guilty of manslaughter, not murder. Lack of mens rea, however, should not be confused with mistake of law or fact. Generally, the maxim “ignorance of the law is no excuse” is valid. It is not a defense to a crime that the perpetrator was not aware of the fact that his or her conduct was unlawful.

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