In the U.S. legal system, people may be punished for a crime only if they've been convicted of a crime—that is, found criminally liable. This article discusses what constitutes criminal liability. For a discussion of civil liability, see our article on Civil Liability.
Lawmakers, technically, decide what is a crime. No act is a crime until it is recognized as such by society and written into the states' and federal criminal codes. We may think certain acts have always been crimes or are treated as crimes everywhere, but that is not the case. For example, U.S. law historically did not recognize the rape of a wife by her husband until relatively recently.
An act is a crime only if a state or the federal government defines it as one. In most states, crimes are classified as either felonies (more serious crimes) or misdemeanors (less serious crimes).
Criminal liability refers to responsibility for a crime and the penalty society imposes for the crime. Because crimes cause harm to society as a whole (in addition to the victim(s)), a government lawyer (prosecutor) brings charges against the offender on behalf of its citizens.
A person can be found liable for a crime if the prosecution proves that the person committed the criminal act (such as stealing) and had the required intent to hold the person accountable (such as intent to deprive the owner of the property).
In order to hold someone to account for a crime, the prosecutor must prove that they harbored the required level of criminal intent (called mens rea). In the example above, the prosecutor must prove that the defendant intended to wrongfully deprive the rightful owner of the property when the defendant took control of it.
In a civil case, by contrast, no criminal intent is required. Many civil actions involve allegations that the defendant acted negligently and, as a result, harmed the plaintiff. The reason for the distinction is that civil cases involve disputes between individuals, not acts against society as a whole. And the possible penalty to the defendant in a civil case is limited to monetary damages or enforcement of certain rights but not imprisonment.
Usually, criminal liability rests upon the person who directly committed the act. But, liability for a crime can reach beyond those directly involved in a criminal act. For example, "felony murder" laws make those involved in a felony that results in a death liable for the death even if they did not "pull the trigger" or otherwise directly cause the victim's demise (such as the getaway driver who helps accomplices flee a botched armed robbery).
In order to convict a person of a crime, the state must usually prove liability in addition to the fact that an act occurred. In other words, in order to prove theft, the state must prove that the defendant took property belonging to another and that the defendant took the property with the intent to deprive the owner of it. But, in the case of a strict liability offense, the prosecution need only prove the person engaged in certain conduct.
Strict liability is the exception in criminal law, not the rule. The rationale for strict liability crimes is that certain acts justify imposing criminal liability regardless of intent. Examples range from public safety offenses (like traffic laws) to offenses involving societal or moral harm (like statutory rape). A person may be convicted of statutory rape even if the victim consented to the sexual contact and, in some states, even if the defendant did not know the victim was underage.
Criminal liability law also recognizes situations in which the person who personally and directly engaged in the criminal act should not be held liable for the crime. Essentially, even though certain people committed a criminal act, they should not be held to account for it. The most obvious example is that of a person who is not guilty of a crime by reason of mental incapacity. Another group exempted from certain criminal liability is minors. The rationale for exempting such individuals from liability is that these people are unable to form the type of intent required to make it fair to hold them to account for the crime.
A person found criminally liable by being convicted of a crime may be sentenced to serve time in jail or prison, to pay a fine, or both. In most states, felonies can be punished by a year or more in prison and misdemeanors by less than a year in jail. In addition (or alternatively), the sentencing judge may order the person convicted to undergo drug or alcohol treatment, anger management or other counseling, and/or to abide by terms of probation (such as drug testing). A person convicted of certain sex crimes might be required to register as a sex offender and abide by other terms upon release, such as periodic reporting to local authorities and staying away from schools, playgrounds, and other facilities where children are present.
The law on criminal liability varies depending on the particular crime charged, the jurisdiction in which the person is charged, and other factors specific to the situation (such as the defendant's age). For questions about what is required to hold someone liable for a certain crime, check the article on that crime and in the state in question on this site.