The act or omissions that comprise the physical elements of a crime as required by statute. See, e.g. Schad v. Arizona, 501 U.S. 624 (1991). The actus reus includes only the willed bodily movements (i.e. voluntary acts). Thus, if a defendant acted on reflex, then the defendant's conduct does not satisfy the actus reus requirement.
The actus reus requirement can also be satisfied by an "omission"; if an individual had a duty to act, and failed to discharge that duty, the individual could be held criminally liable for the result. Generally, for the purposes of criminal liability, an individual is under a duty to act if:
- A statute requires a person to act in a certain way. For example, if a statute required doctors to keep patients on life support indefinitely, cutting life support would be a breach of statutory duty.
- A contract requires a person to act in a certain way. Take an individual who contracts with a bodyguard to protect the individual from threats on his or her life; if the bodyguard notices the threat and willfully ignores it, the bodyguard could be found criminally liable.
- Some special status relationship exists that creates a duty to act in a certain way. A mother who neglects to feed her child, for example, breaches a duty based on the parent-child relationship.
- Voluntary assumption of care creates a duty to act in a certain way. If an individual comes across another in distress and offers to help but later abandons the one in distress, the individual could be held criminally liable.
- The individual created the risk, he or she must act to prevent harm. For example, take an individual who left his or her car on a hill with breaks disengaged. If the car begins rolling towards pedestrians at the bottom of the hill, the individual has a duty to stop the car.
The statutory definition of a crime pairs Actus Reus with Mens rea, the psychological state defining a criminal perpetrator as culpable for having committed a crime.
See criminal law