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Actus Reus: The Physical Act of Committing a Crime

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Actus Reus: The Physical Act of Committing a Crime

Criminal liability will require proof of a physical act prior to any discussion of criminal mental states.[1] This physical act requirement is known as actus reus and is a foundational concept of American criminal legal doctrine.[2]

This presentation explores actus reus and affirmative acts, as well as defining when a failure to act may lead to a defendant’s criminal liability.

Example of Actus Reus

The actus reus component of a crime will vary depending on the crime and the state where the defendant is being prosecuted.

For example, burglary in Illinois is defined as, “[a] person commits burglary when without authority he or she knowingly enters or without authority remains within a building, housetrailer, watercraft, aircraft, motor vehicle, railroad car, or any part thereof, with intent to commit therein a felony or theft.”  To show that the actus reus element is satisfied, the prosecution will have to prove that the defendant unlawfully entered, or remained in, the building without authority, and that he intended to commit a felony or steal therein.

When is Actus Reus satisfied?

For the actus reus element of a crime to be present, there must be a voluntary, physical action made by the defendant. The prosecution must prove the defendant made a conscious and intentional movement.  Additionally, a person can be held criminally responsible if he engages in an action, knowing that he may unintentionally become unconscious and hurt somebody.[3] In one case, a New York state appeals court held a defendant was criminally responsible for his actions because he knew that he was subject to epileptic attacks rendering him likely to lose consciousness. Thus, he was responsible for the harms caused while suffering an epileptic episode and driving his automobile over a sidewalk, resulting in the death of four people.

When is Actus Reus NOT satisfied?

Historically, when a law criminalizes a status or illness (such as drug addiction or alcoholism), that law has been found to be unconstitutional because the law may result in cruel and unusual punishment.  The United States Supreme Court held that someone could not be arrested and charged with being a drug addict because being a drug addict is a status, not an action.

Second, criminal thoughts do not satisfy the actus reus element. Criminal thoughts, if not accompanied by any action, do not harm society in any way and will not lead to criminal liability. 

Does a failure to act satisfy actus reus element?

            A failure to act, known as an omission, could satisfy actus reus and potentially give rise to criminal liability. In order to do so, the prosecution must prove the following three elements:

            (1)  There was a legal duty to act;

            (2)  The defendant knew that he had a legal duty to act; and

            (3)  It was reasonable for the defendant to perform the duty or the defendant was physically capable of performing the legal duty

A legal duty to act arises in five situations. The first is when there is a special relationship between the defendant and the victim. These special relationships include parent-child relationships, employer-employee relationships, or husband-wife relationships.[4] The second situation that forms a legal duty to act is one that is imposed by law or by legislation.[5] The third method of creating a legal duty to act is through a private contract between parties. In a case highlighting this legal duty to act, defendants were found guilty of murder in the third degree after the death of a 92-year old man who lived with the defendants.[6] The Pennsylvania Supreme Court reasoned that actus reus was satisfied because the defendants had an oral contract to provide food and medical care to the deceased. Their failure to perform their part of the oral contract gave rise to an omission. Lastly, a legal duty to act will arise if the defendant wrongfully created the peril for the victim. If the defendant wrongfully places the victim in danger, then his failure to help the victim could lead to criminal liability.

            It is important to understand that there is no criminal liability for an omission when there is only a moral obligation to act. A party is not bound to perform or prevent harm to another “simply upon his humanity, or his sense of justice or propriety.”[7] In People v. Beardsley, the Michigan Supreme Court approached the issue of whether the defendant, who was convicted of manslaughter, had a legal duty to act to save the victim who overdosed on morphine in his presence. The court held that the man could not be convicted because he had no legal duty to take reasonable measures to prevent her death, even though saving her life was the right thing to do.

Actus reus will have to be proven alongside of mens rea in order to secure a conviction. Once both elements are, a jury can reasonably reach the conclusion that a guilty verdict is appropriate.


[1] Robinson v. California, 370 U.S. 660, (1962).

[2] Ian Farrell, Taking Voluntariness Seriously, 54 B.C. L. Rev. 1545, (2013).

[3] People v. Decina, 138 N.E.2d 799, (N.Y. Ct. App. 1956).

[4] Roberts v. St. Louis & S. F. R. Co., 136 Kan. 749, 18 P.2d 167, 1933 Kan. LEXIS 21 (Kan. 1933)

[5] Francis McCarthy, Crimes of Omission in Pennsylvania, 68 Temp. L. Rev. 633, (1995). 

[6] Commonwealth v. Pestinikas, 421 Pa. Super. 371, 617 A.2d 1339, 1992 Pa. Super. LEXIS 4260 (Pa. Super. Ct. Dec. 10, 1992)

[7] People v. Beardsley, 150 Mich. 206, 113 N.W. 1128, 1907 Mich. LEXIS 779 (Mich. 1907)