In criminal law, Actus reus (), Latin for "guilty act", is one of the elements normally required to prove commission of a crime in common law jurisdictions, the other being mens rea ("guilty mind"). In the United States it is sometimes called the external element or the objective element of a crime.
Etymology
The terms actus reus and mens rea developed in English Law are derived from a principle stated by Edward Coke, namely, actus non facit reum nisi mens sit rea, which means: "an act does not make a person guilty unless (their) mind is also guilty"; hence, the general test of guilt is one that requires proof of fault, culpability or blameworthiness both in thought and action.
Act
In order for an actus reus to be committed there has to have been an act. Various common law jurisdictions define act differently but generally, an act is a "bodily movement whether voluntary or involuntary." In Robinson v. California, , the U.S. Supreme Court ruled that a California law making it illegal to be a drug addict was unconstitutional because the mere status of being a drug addict was not an act and thus not criminal. Commentator Dennis Baker asserts:
An act can consist of commission, omission or possession.
Omission
Omission involves a failure to engage in a necessary bodily movement resulting in injury. As with commission acts, omission acts can be reasoned casually using the but for approach. But for not having acted, the injury would not have occurred. The Model Penal Code specifically outlines specifications for criminal omissions:
the omission is expressly made sufficient by the law defining the offense, or
a duty to perform the omitted act is otherwise imposed by law (for example one must file a tax return).
Hence, if legislation specifically criminalizes an omission through statute, or a duty that would normally be expected was omitted and caused injury, an actus reus has occurred.
In English law, there is no Good Samaritan rule therefore one cannot be criminally liable for an omission unless a duty of care is owed. An omission can be criminal if there is a statute that requires one to act. A duty of care is imposed and one is required to act when one is: under a contract (R v Pittwood), has assumed care (R v Stone and Dobinson), has created a dangerous situation (R v Miller), or fails to perform one's official position (R v Dytham.).
Possession
Possession holds a special place in that it has been criminalized but under common law does not constitute an act. Some countries like the United States have avoided the common law conclusion in Regina v. Dugdale by legally defining possession as a voluntary act. As a voluntary act, it fulfills the requirements to establish actus reus.
Voluntariness
For conduct to constitute an actus reus, it must be engaged in voluntarily. Few sources enumerate the entirety of what constitutes voluntary and involuntary conduct. Oliver Wendell Holmes, in his 1881 book The Common Law, disputed whether such a thing as an involuntary act exists: "[a] spasm is not an act. The contraction of the muscles must be willed." A few sources, such as the Model Penal Code, provide a more thorough treatment of involuntary conduct:
a reflex or convulsion; a bodily movement during unconsciousness or sleep; conduct during hypnosis or resulting from hypnotic suggestion; a bodily movement that otherwise is not a product of the effort or the determination of the actor, either conscious or habitual.