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 York, 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 element of a crime. This means that the individual's actions or inactions must be deliberate and lead to the fulfillment of the crime's statutory elements. For instance, if a person is legally obligated to provide care to another and fails to do so, resulting in harm, this omission could be considered actus reus if it meets the criteria of a specific criminal offense. On the other hand, mens rea refers to the mental state of the defendant at the time of the crime. New York law recognizes various levels of mens rea, such as intent, knowledge, recklessness, and negligence, which correspond to the defendant's state of mind regarding their actions or the consequences of their actions. Both actus reus and mens rea are typically required to establish criminal liability, although there are exceptions for strict liability offenses where mens rea is not a necessary component.