Actus reus is the act—or the omission or failure to act when there is a duty to act—that comprises the physical elements of the commission of a crime. The actus reus generally must be voluntary bodily movements that constitute a crime.
In contrast, mens rea (meaning “guilty mind”) is the criminal intent element of a crime. It is the intent to commit a crime, or the knowledge that the action, or failure to act when there is a duty to act, will result in the commission of a crime.

In Arizona, as in other jurisdictions, the concept of actus reus requires that a defendant must have engaged in a voluntary act, or an omission when there is a legal duty to act, that constitutes the physical elements of a crime. This means that for a person to be found guilty of a crime, there must be evidence of their physical conduct that breaches the law. This conduct could be an action, such as striking another person, or a failure to act, such as not providing food to a child when legally obligated to do so. On the other hand, mens rea refers to the mental state of the defendant at the time of the crime. Arizona law recognizes various forms of mens rea, including intentionally, knowingly, recklessly, and with criminal negligence. The presence of mens rea means that the individual had the intent to commit the crime or was aware that their actions could lead to a criminal outcome. Both actus reus and mens rea are required elements that must be proven beyond a reasonable doubt for a conviction in a criminal case.