Principles of Criminal Liability

A crime has been charged. The defendant pleads not guilty. What must the government prosecutor prove? Why?

There are basic principles underlying the prosecution of a crime. A crime is composed of elements. These elements include a mental state, prohibited action and lack of legal justification. Each of these elements must be proven by the government beyond a reasonable doubt. If any element is not proven, the person charged must be found not guilty.

Mens Rea, The Guilty Mind

An element of every crime (with the exception of *“strict liability”), is a state of mind. This state of mind is referred to as mens rea. This is Latin for “guilty mind”. Mens rea is the defendant’s state of mind when he engages in prohibited conduct.

The primary source in most American jurisdictions for defining mens rea is the American Law Institute’s Model Penal Code. The code sets four standards. Guilt can be attributed to an individual who acts “purposely,” “knowingly,” “recklessly,” or “negligently.” Statutes give additional definition to these concepts and set forth which mental state applies to a particular crime.

When someone acts consciously to cause a particular result, he acts “purposely”. An act is done “knowingly” when the actor is aware that his conduct has a high probability of a specific result. When an individual disregards an unjustifiable risk an action is done “recklessly”. If someone has grossly deviated from the standard of care of a reasonable person he has acted “negligently”.

Actus Reus, The Criminal Act

There is no punishment for thinking about a criminal act. A crime must have an actus reus, Latin literally for a bad act. A defendant has committed the actus reus of an offense if he has done some act that is an action prohibited by law. Most crimes consist of a defined set of actions that together are prohibited.

It is not a crime to carry an item around a store. It is not a crime to walk out of a store. It may be a crime to walk out of a store, with an item, and not pay for it. The act of walking out of the store without paying for an item is the actus reus. For it to be a crime, it must be done knowingly. The actus reus and the mens rea must take place together.

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Concurrence of Mens Rea and Actus Reus Required

In the example above, it is possible that a person was without a shopping cart, arms full and for convenience used a pocket to hold an item. He pays for all the other goods and forgets about what is in his pocket, leaving the store. There has been no crime. There was an actus reus, but there was no mental state to commit the bad act existed as he left the store.

Mens rea and actus reus must exist simultaneously. Thinking about committing a crime without doing so cannot be punished. Doing a prohibited act without having criminal intent is not criminal. The action and intent must take place together.

The existence of a concurrence of mens rea and actus reus is decided by the fact finder, either a judge or a jury. This is done by presentation of evidence, either direct or circumstantial.

Legal Excuse: The Affirmative Defense

A person can commit a prohibited act with the mental state required by law and still not be guilty of a crime. This is because there was a legal excuse or justification. This is known as an affirmative defense.

Some affirmative defenses are:

  • Insanity
  • Entrapment
  • Self defense
  • Defense of others
  • Necessity
  • Duress
  • Involuntary intoxication

Beyond a Reasonable Doubt

For the government to prove that someone is guilty of a crime, it must be shown beyond a reasonable doubt:

  • A prohibited act (actus reus)
  • The defined mental state (mens rea)
  • There was no legal excuse

The procedure involved in charging criminal activity and conducting criminal prosecutions is discussed in the Felony Process. The principles for finding criminal liability apply to any crime whether it is a felony or a misdemeanor.

*Strict liability applies generally in relatively minor offenses. An example would be a speeding ticket. All the government need show is the speed limit, the car’s speed and who was driving. The driver’s knowledge of the limit and the speed are not needed for a finding of guilt.


For Further Reading



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