Murder, or criminal homicide, usually distinguished from manslaughter by the element of malice aforethought. The law presumes the existence of malice aforethought from the circumstances, and it does not necessarily have to be proved directly. The most clear-cut case of this presumption of malice is when the killer inadvertently murders a person other than his intended victim.

Murder in the first degree generally is a calculated act of slaying committed with malice aforethought, often requiring aggravated circumstances such as extreme brutality.

Second-degree murder is a homicide committed with malice, but without deliberation or premeditation. A homicide committed without malice (as in negligent motor vehicle operation) or in the “heat of passion” (as in a quarrel which escalates to violence) is generally considered manslaughter.

In some cases, it is difficult to determine whether malice aforethought was present; consequently the governor of a state (or other chief executive) not infrequently uses his power of commutation of sentence to revoke the death penalty, and in some states the appellate courts automatically review all convictions of murder.