murder, in criminal law, the killing of one person by another that is not legally justified or excusable, usually distinguished from the crime of manslaughter by the element of malice aforethought.
The term homicide is a general term used to describe the killing of one human being by another. A murder is considered a homicide, but homicide can also refer to a killing deemed justifiable or excusable. All legal systems make important distinctions between types of homicide, and punishments vary substantially according to the killer’s intent, the circumstances of the homicide, and other factors.
Common-law codes define murder as a homicide committed intentionally or as a result of the commission of another serious offense. By contrast, the crime of manslaughter includes killings that are the result of recklessness or violent emotional outbursts. Penalties for murder are substantially more severe than those for manslaughter and may include capital punishment or life imprisonment.
Common-law systems require an element of intent (malice aforethought, or mens rea) in order to classify a killing as a murder. This includes “transferred intent”—as when one who intends to kill another kills a third person by mistake—and intent that may be inferred from the extreme recklessness or dangerousness of the act. Many U.S. states distinguish between murder of the first, second, and third degree, with capital punishment limited to crimes of clear intent.
Civil-law codes group all unjustified killings under the single crime of homicide. Penalties are determined based on the circumstances of the act, and they vary across countries. Civil law of the European tradition, like common law of the Anglo-American tradition, distinguish between intentional and other felony murders on the one hand and reckless, negligent, and provoked murders on the other. In all systems, the most important distinction relevant to sentencing is that between conduct that is socially dangerous—that demonstrates intent to kill, in other words—and conduct that is merely reckless.
Civil-law codes also place a greater emphasis on the dangerousness of the killer’s conduct and the circumstances surrounding the act. Bodily injury that results in death as well as a death that is the result of negligence rather than recklessness are two examples of homicides that are more heavily penalized in civil-law systems than in common-law ones. Civil-law codes often punish any killer as a murderer if the culprit has employed a deadly weapon, but in England, for example, death resulting from a felony is defined as murder only in the case of certain serious crimes, such as robbery or rape.
The terms serial murder and mass murder refer to the unlawful homicide of multiple people by the same person. Definitions of these terms are debated, and neither are formally recognized in legal codes. These murders, and the people who commit them, generate tremendous amounts of public attention. Mass shootings, when fatalities occur, are a form of mass murder. Assassinations are a particularly high-profile type of murder.