We have already looked at the requirement that a criminal defendant commit an act before he can be found guilty of a crime. We can now turn our attention to whether a criminal defendant can commit a crime by an omission or by failing to act.

The Model Penal Code or MPC, which is an example of laws that are used by state legislatures in drafting criminal statutes, addresses this issue. The MPC says that a person is not guilty of any offense unless his conduct “includes a voluntary act or omission to perform an act of which he is physically capable.” According to the MPC, liability based on an omission is permitted in two circumstances: if the law defining the offense provides for it or if the duty to act is otherwise imposed by law.

As with the MPC, generally, state law provides that there is no duty to act and failing to act cannot result in criminal liability. Someone whose omission harms another person usually cannot be held criminally liable for the omission.

This general proposition gives way when the circumstances are such that the omission would result in grave physical harm to another person. Criminal statutes specify what level of harm is necessary to trigger the statute.

This exception to no-liability only arises when the criminal defendant owes a legal duty to the third party. A duty can be created by common law, statute, or by contract. These duties arise in relationships founded on the dependence of one party on the other or on their interdependence. For example, common law provides that innkeepers have certain duties with regard to their residents, doctors have certain duties with regard to their patients, spouses have certain duties with respect to their spouses, and parents have certain duties with regard to their children.

A duty can also arise out of an action taken by the criminal defendant. For example, in some circumstances an act, followed by an omission, will result in criminal responsibility for the omission even when there is no liability for the act. This happens when the criminal defendant creates the risk or provides voluntary assistance to someone in jeopardy.

With regard to creating a risk, a person who wrongfully, or perhaps even innocently, harms another or another’s property, or who places a person or her property in risk of harm, has a common law duty to aid the injured or endangered party.

With regard to voluntary assistance, one who voluntary commences assistance to another in jeopardy has a duty to continue to provide aid, at least if a subsequent omission would put the victim in a worse position than if the actor had not initiated help.

The duties stemming from creating the risk and voluntary assistance often arise in the context of providing medical care. This type of situation is typified by the California Court of Appeals decision in Barber v. Superior Court.

In Barber, the defendants treated a patient who had suffered a heart attack after surgery. The patient was in a vegetative state. After consulting the family, the doctors ordered the removal of the ventilator and then the removal of intravenous feeding tubes. The patient died. The doctors were charged with murder.

The court held that the cessation of “heroic” life support measures and the administration of intravenous nourishment and fluids are not affirmative acts, but rather withdrawals or omissions of further treatment. With regard to the legal duty, the court found that although there may be a duty to provide life-sustaining machinery in the immediate aftermath of the heart attack, there is no duty to continue its use once it has become futile in the opinion of the qualified medical personnel.

The court reasoned that the determination should be based on whether the proposed treatment is proportionate or disproportionate in terms of the benefit to be gained versus the burdens caused.

In the end, the court held the criminal defendant’s omission to continue treatment under the circumstances, though intentional and with knowledge that the patient would die, was not an unlawful failure to perform a legal duty.

Thus, a voluntary act, involuntary act, or omission can result in criminal liability. These actions satisfy the means rea or required act element for criminal law statutes. In addition to the required act, most criminal law statutes also require a mental state for the imposition of criminal liability. Let’s look at the required mental state for criminal liability now.