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 New Jersey, as in other jurisdictions, the concept of actus reus requires that a defendant must have engaged in a voluntary act, or a failure to act when there is a legal duty to do so, 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 actual conduct that breached the law. This conduct could be an action, such as striking another person, or an omission, such as failing to provide 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. New Jersey law recognizes various levels of mens rea, including purposeful, knowing, reckless, and negligent states of mind. For a conviction, the state must typically prove that the defendant had the requisite level of criminal intent or was aware of their conduct that would lead to the commission of a crime. Both actus reus and mens rea are fundamental components that must be established for a criminal offense, except for strict liability offenses where mens rea is not required.