Actus reus (Latin: "guilty act") refers to the external, physical elements of a criminal offence. It is contrasted with mens rea, the mental element. To secure a conviction, the prosecution must normally prove both, and show that they coincided.
Components
The actus reus may consist of conduct (for example, taking property), circumstances (for example, that the property belongs to another), and results (for example, death in a homicide). Not every offence has all three: some are complete on the conduct alone, while others require a particular consequence.
Voluntariness
Conduct must be voluntary. A person who acts during an epileptic seizure, or who is physically forced by another, does not commit the actus reus in the relevant sense.
Omissions
As a general rule, criminal law punishes acts rather than failures to act. A failure to act can, however, amount to the actus reus where the law imposes a duty, such as that of a parent towards a child, an employee under contract, or a person who has created a dangerous situation.
Causation
For result crimes, the conduct must cause the result in fact (the result would not have occurred but for the conduct) and in law (the conduct must be a significant and operating cause, not broken by an independent intervening act).
In Indonesian Doctrine
Indonesian criminal law describes the objective elements of an offence as the unsur objektif, set against the subjective elements of fault. Together they make up the elements (unsur-unsur) that a prosecutor must set out in the indictment and prove at trial.