Criminal Law


Crime generally refers to particular acts that violate laws as designated by a government, and which therefore are deserving of punishment. Frequently, such acts fall in the category of behavior that violates social mores. For criminals, the violators of the criminal law, punishment may come in the form of a fine, imprisonment, or, in the most serious cases, death. Since the Enlightenment, modern theorists have offered several justifications—some dating back to medieval and even ancient times—for the imposition of punishments for breaking the criminal law. One common justification is retribution: because the criminal broke the law, it is only fair or just that he or she suffer negative consequences. Deterrence, another justification, is the concept that the potential for punishment may dissuade would-be criminals from engaging in illegal behavior. Other justifications assign avalue to imprisonment, such as protection—imprisonment of criminals protects society from further criminal acts through incapacitation—and rehabilitation—time in prison may make criminals see the error of their ways and decide to obey the law. A final justification for punishment, restoration, seeks to redress the suffering of the victim through punishment of the offender.

In the United States, though both states and the federal government have the ability to punish individuals for crime, the vast majority of crimes are prosecuted at the state level as part of each state's criminal code. Many state codes had their roots in the English common law. After American independence, the influence of Thomas Jefferson, among others, led to the codification (collection and classification) of criminal law so as to remove lawmaking decisions from the courts. In addition to his opposition to the counter majoritarian nature of the common law, Jefferson was opposed to the common law's felony murder rule, and created a draft model criminal statute for Virginia which was eventually adopted by the Commonwealth.

Legislatures are responsible for the creation of the criminal law in the United States. In 1962 the American Law Institute, based on its examination of all the individual state codes, created the Model Penal Code (MPC), a standardized statutory text. The MPC identifies an important objective of criminal law as “to give fair warning of the nature of the conduct declared to constitute an offense.”


In the American system a crime has two main parts, or elements: conduct (actus reus, literally “guilty act”) and intent (mens rea, literally “guilty mind”). The American actus reus tradition grew out of problems with the English common law, under which certain crimes, such as treason, could be punished because of an individual's thoughts alone in the absence of any action. The Framers recognized the problem of establishing intent (as opposed to desire), and were reluctant to punish individuals for thoughts they may never have acted on. As Ian Farrell and Justin Marceau ( 2013 ) note, the American system thus establishes the actus reus requirement: individuals must have engaged in an act to be deemed criminals. Thoughts are not punishable by criminal law.

Actus reus may also entail the omission of an action if there was a legal requirement to act that the offender ignored. The act or omission must be made voluntarily by the offender; action as result of a seizure, for example, is not considered voluntary. Similarly, an omission will be involuntary if the person with a duty to act is incapable of the action. It is possible for a person to break the law without being aware of having done so. For example, a person could commit the actus reus accidentally.

As Martin Gardner ( 1993 ) points out, the mens rea requirement for guilt emerged in the thirteenth century. It was created to satisfy the sense that, for justice and fairness to be achieved, people must deserve their punishments. As a result, even if a person has engaged in criminal conduct, he is not guilty of the crime unless he has the requisite mental state, or mens rea. The mental state requirement applies to the person's intent regarding his conduct and not his intent to break the law.

Reflecting the idea that there are varying degrees of culpability, or blameworthiness, mens rea has different levels. In order from most to least culpable, the mental states are purposely, knowingly, recklessly, and negligently. Purposely means the offender acts with the goal of breaking the law. Knowingly means the offender is aware of the circumstances and knows or is practically certain the action will result in breaking the law. Recklessly means the actor is aware of a significant risk that her actions will cause the crime and ignores this risk. Negligently means the actor is unaware of this risk but that a reasonable person would be aware of this risk and not take it. In general, greater levels of culpability merit more severe punishment.

A small number of crimes, called strict liability crimes, do not have mens rea requirements. One example is a parking violation: the government does not need to prove that the driver parked the car illegally with any particular level of intent. Another example is statutory rape, in which an offender may be liable in the absence of specific knowledge that the victim is under the age of consent.


Some crimes require causation. For example, to be guilty of the crime of homicide, the offender's conduct must cause the criminal harm—the death of another person— that the statute prohibits. There are two types of causation, actual and proximate, and both must be met for an action to be criminal.

Actual cause, also called “cause in fact,” is generally determined by the “but for” test. This test is satisfied if but for the offender's conduct the harm would not have resulted. Although the individual may not technically cause the harm, in some cases actual cause may be satisfied. For instance, consider a situation in which two armed individuals are shooting at the same victim at the same time. The bullet shot by one of the two gunmen strikes the victim in the head, the other bullet goes through the victim's heart. Either gunshot would have been sufficient to kill the victim, so neither gunman's action passes the “but for” test; but both actors' conduct would be the actual cause of the death. Similarly, consider a situation in which two persons were working independently, whose actions were insufficient by themselves to cause the resulting bad outcome, but that, combined, did lead to criminal harm. In such a case, if any actor's conduct is a substantial factor in the criminal result, then it is an actual cause of that result.

Proximate cause, or “legal causation,” protects the accused from being held responsible for results that are too far removed from the accused's conduct. When an actor's conduct is directly connected to the resultant harm, without any interference by the victim or a third party, proximate cause is established. If there is interference, the actor's conduct may or may not be a proximate cause. If the interference contributes to the cause, the original conduct is a proximate cause. If the interference independently causes the result or substantially accelerates it, the original conduct has been superseded and is not a proximate cause of the result.


Committing an act with the requisite mens rea is not the last step for assigning punishment. Mental capacity can affect one's liability for criminal conduct. Individuals who are determined to be suffering from a mental disorder and those too young to understand the consequences of their actions may not be held criminally responsible.

A person accused of a criminal offense can present defenses against the charges. Defenses can exonerate the accused or prevent conviction; in the case of conviction, defenses can reduce either the severity or duration of the accused's punishment. As Paul Robinson observes ( 2002 ), defenses bring a sense of fairness to criminal proceedings by allowing the particular circumstances surrounding the offense to be considered in determining whether the individual should be punished for the crime.

Some defenses present justifications. Justifications maintain that the accused's actions were right and proper, and that her actions were not blameworthy but rather serve justice. Justifications include self-defense or the defense of others. Another common justification is necessity, which allows that a person's unlawful act or acts were committed in order to prevent a greater harm. An example of the necessity defense is trespassing on a property owner's land as a means to avoid an automobile accident. Necessity cannot be used, however, to justify killings.

Other defenses present excuses. As distinguished from justifications, excuses maintain not that the committed act was good but that there is a reason why the conduct should not be punished as usual. The insanity defense is an excuse: the killing of an individual by an insane person is not a justifiable good action, but because of the actor's insanity it is not proper to punish the actor as a sane person would be punished.

As Robinson notes, most criminal defenses have remained relatively unchanged since the beginning of the eighteenth century. Others, however, were developed more recently. The clinical psychologist Lenore Walker is credited with having first identified battered spouse syndrome (which she referred to as battered woman syndrome) in the 1970s. In cases where women are accused of killing or harming their spouses, defense attorneys often obtain expert testimony regarding battered spouse syndrome, concentrating on the batterer's abuse and the defendant's low self-esteem and other psychological and emotional issues. Because of the syndrome, the defendant may have come to believe that her spouse was about to kill her and thus to have acted based on that belief, even in a nonconfrontational setting. Most jurisdictions now allow introduction of evidence of battered spouse syndrome where relevant to claims of self-defense.


Three men stand in a police lineup, a procedure used to confirm the identity of a suspect.

Three men stand in a police lineup, a procedure used to confirm the identity of a suspect.

In many jurisdictions murder is separated into two degrees, or levels. First-degree murder involves a killing that was willful, deliberate, premeditated, or committed during the course of other serious felonies, such as rape or arson. Second-degree murder is composed of the unlawful homicides committed with malice that do not satisfy this additional requirement.

Manslaughter is often divided into voluntary and involuntary manslaughter. Voluntary manslaughter is intentional but committed without malice. It may be committed in the heat of passion after the killer was provoked. Involuntary manslaughter is identified as an unintended killing that results from the actor's unlawful activity that is not a felony or the actor's lawful activity that was carried out negligently.

Nearly every state has some version of the felony murder rule, which makes one guilty of murder if death occurs in the commission of a felony. Depending on the felony being committed, under this rule one could be convicted of first- or second-degree murder. The felony murder rule, which has been much criticized, may come into force irrespective of issues of foreseeability, intent, or malice. In other words, as Wayne LaFave ( 2003 ) notes, this rule may apply irrespective of whether a felon kills intentionally, recklessly, negligently, accidentally, or unforeseeably.

Homicide Statutes in Early America. Homicide statutes developed distinct from the common law in early America. According to Guyora Binder ( 2004–5 ), half of the American colonies had homicide statutes, and most colonies sentenced offenders guilty of “willful” or “malicious” murder to death. Classifying murder as first or second degree began in Pennsylvania in 1794, out of the desire to limit the death penalty to only “deliberate assassination.” Degrees of murder originated in America and were not brought over from English common law. The Pennsylvania system was adopted, in some cases with and in other cases without changes, in thirty-one other states by 1900.


Since the late twentieth century, legal and political debates have concerned the subjects of overcriminalization—the proliferation of criminal statutes—and “stand your ground” laws, which alter the common law by taking away the duty to retreat.

Overcriminalization. The number of state and federal criminal statutes has increased so significantly since the 1980s that it is sometimes difficult for experts to identify precisely how many criminal laws exist. As Susan Ehrlich highlights, in the 1980s and 1990s several federal criminal statutes have been passed by Congress in response to high profile crimes. For instance, one highly publicized case in 1992 involved a Maryland woman who died after her arm became tangled in the seatbelt, and her carjacker drove off, dragging her behind the car. Just one month after this Maryland carjacking, Congress passed a law making carjacking a federal crime, with a minimum sentence of 15 years. John Baker ( 2004 ) observes that experts attempting to quantify federal criminal statutes have identified more than 4,000 violations in the federal criminal code by Congress. This does not include federal regulations with criminal penalties have been created by federal agencies, such as the Environmental Protection Agency. State legislatures have similarly expanded their state criminal codes, adding statutes criminalizing a large number of activities not traditionally treated as crimes. For instance, in Texas, as Marc Levin ( 2008 ) notes, there are eleven felonies that can be committed in the harvesting and handling of oysters. Scholars argue that overcriminalization leads to a variety of ills, including prison overcrowding, clogging the lower criminal courts, and frivolous arrests. In 2006 a twelve-year-old girl was arrested for eating French fries in a Washington, DC, metro station.

One major problem of overcriminalization is the sheer number of individuals prosecuted for crimes. Drug crimes have been the focus of much attention by legislatures and as a result by prosecutors. The number of individuals prosecuted and incarcerated for drug crimes has grown exponentially. Not all of these drug crimes are violent. According to Susan Klein and Ingrid Grobey ( 2013 ), in 2006 in the United States 165,534 people were convicted of felony drug possession. The vast majority— some 99 percent—of those convicted were convicted of state crimes.

Scholars argue that overcriminalization has had especially negative consequences for members of minority groups. According to the US Bureau of Justice Statistics, approximately one in every three African American males can expect to go to prison at some point in their lifetime. Michelle Alexander ( 2010 ) argues that this particular ramification of overcriminalization, particularly in the area of drug laws, has led to the mass incarceration of young black men and labels the phenomenon the “new Jim Crow.” The implications for people of color caught up in the criminal justice system are significant as they face discrimination upon release and are more likely than nonwhites to be returned to the system, either because of further criminal activity or violating the terms of parole.

Stand Your Ground Laws. Many jurisdictions have enacted “stand your ground” or “make my day” laws, which provide immunity from criminal prosecution or tort immunity to individuals who defend themselves in a particular set of circumstances. If, for example, one is engaged in lawful activity (e.g., walking down the street) and confronted by a threatening assailant, there is no duty to avoid confrontation, as would be the case under the common law.

Like the common law, stand your ground statutes require proportionality—force must be met with similar force. According to Jay Zitter ( 2012 ), if deadly force is used, the individual seeking justification must have a reasonable belief that deadly force was required to prevent the commission of a felony, death, or serious bodily harm to himself or another.

Stand your ground laws around the United States were called into question after the 2012 killing of Trayvon Martin by George Zimmerman in Sanford, Florida. Martin, an unarmed high school student who was out walking after buying food at a store, was confronted by Zimmerman, a neighborhood watch volunteer who was armed. Relying on Florida's stand your ground law, police officers initially did not arrest Zimmerman, who claimed that he had shot Martin in self-defense. Zimmerman was later charged with and acquitted of both second-degree murder and manslaughter. Though Florida's stand your ground law was not at issue in Zimmerman's trial, the fact that he was initially not charged because of the law and therefore might have escaped any sort of legal inquiry, critics of stand your ground laws have called for their repeal in jurisdictions around the country.

SEE ALSO Common Law ; Constitutional Criminal Procedure ; Federalism in American History ; Fourth Amendment ; Police Powers ; US Bill of Rights .


Alexander, Michelle. The New Jim Crow: Mass Incarceration in the Age of Colorblindness. New York: New Press, 2010.

Baker, Dennis J. The Right Not to be Criminalized: Demarcating Criminal Law's Authority. Burlington, VT: Ashgate, 2011.

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Dressler, Joshua. “Justifications and Excuses: A Brief Review of the Concepts and the Literature.” Wayne Law Review 33, no. 4 (1987): 1155–67.

Ehrlich, Susan. “The Increasing Federalization of Crime.” Arizona State Law Journal 32 (2000): 825–41.

Farrell, Ian P., and Justin F. Marceau. “Taking Voluntariness Seriously.” Boston College Law Review 54, no. 1 (2013): 1545–612.

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Hladio, Andrew M., and Robert J. Taylor. “Parole, Probation and Due Process.” Pennsylvania Business Association Quarterly 70 (1999): 168.

Klein, Susan R., and Ingrid B. Grobey. “Overfederalization of Criminal Law: It's a Myth.” Criminal Justice 28, no. 1 (2013).

LaFave, Wayne R. Criminal Law. 4th ed. St. Paul, MN: Thomson/West, 2003.

Levin, Marc A. “Business Overcriminalization.” Texas Public Policy Foundation. December 2008. .

Robinson, Paul H. “Criminal Law Defenses: A Systematic Analysis.” Columbia Law Review 82 (1982): 199–291.

Zitter, Jay M. “Construction and Application of ‘Make My Day’ and ‘Stand Your Ground’ Statutes.” 76 American Law Reports 6th 1 (2012).

Jeannine Bell
Indiana University Maurer School of Law