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 Colorado, 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 involuntary actions, such as reflexive or convulsive acts, or actions performed while unconscious or asleep, are generally not considered actus reus. For an omission to be punishable, there must be a statutory or contractual duty to act. Mens rea, on the other hand, refers to the mental state of the defendant at the time of the crime. Colorado law recognizes various levels of mens rea, ranging from intentional and knowing to reckless and negligent conduct. The specific mens rea required for a crime is defined by the statute outlining the offense. Both actus reus and mens rea must be established for a defendant to be found guilty of most crimes, reflecting the principle that a criminal offense is composed of both a 'guilty act' and a 'guilty mind'.