What is a crime?

A crime is an action — or sometimes a failure to act — that breaks a criminal law. Criminal law, as distinguished from civil law, is a system of laws concerned with crimes and the punishment of individuals who commit them.

Where a civil case involves two parties disputing their rights, a criminal prosecution involves the government deciding whether to punish an individual for an act or omission. A "crime" is any act or omission in violation of a law prohibiting that action.

The three elements prosecutors must prove

In general, every crime involves three elements that the government must prove beyond a reasonable doubt.

First, the act or conduct — known as actus reus. Second, the individual's mental state at the time of the act — known as mens rea. Third, causation: the connection between the act and the resulting harm, typically either proximate causation or but-for causation.

According to the Supreme Court in Elonis v. United States (2015), when a statute does not prescribe a specific mental state, a court will infer the mens rea necessary to separate wrongful from innocent conduct.

Criminal codes: federal and state

Each state decides what conduct to designate a crime and has its own criminal code. Congress has also chosen to punish certain conduct, codifying federal criminal law in Title 18 of the U.S. Code. Criminal laws vary significantly among the states and the federal government.

Title 18 designates various conduct as federal crimes, such as arson, use of chemical weapons, counterfeit and forgery, embezzlement, espionage, genocide, and kidnapping. These statutes usually prescribe a maximum sentence for a convicted individual.

The federal government has also codified the specific procedures which must take place during a criminal proceeding in the Federal Rules of Criminal Procedure.

Types of crimes

Crimes can be generally separated into four categories: felonies, misdemeanors, inchoate offenses, and strict liability offenses.

At common law, there were nine major felonies — Murder, Robbery, Manslaughter, Rape, Sodomy, Larceny, Arson, Mayhem, and Burglary — and various misdemeanors such as assault, battery, false imprisonment, perjury, and intimidation of jurors.

Today, state criminal codes are far more extensive. The New York Penal Law, for example, prescribes nine levels of felonies, ranging from residential mortgage fraud in the fourth degree to terrorism. Congress has limited power to make criminal laws, as this power is generally reserved to the states.