A criminal homicide committed with malice is known as murder , otherwise it is called manslaughter . A homicide is excusable if it is the result of an accident that occurred during a lawful act and that did not amount to criminal negligence . Justifiable homicides are intentional killings done in accordance with legal obligation, or in circumstances where the law recognizes no wrong. They include the execution of criminals in some states, killings necessary to prevent a felony or to arrest a suspected felon, and killings in self-defense. In some states of the United States, one may lawfully kill in resisting the unlawful invasion of a home or real property .
Many states make a distinction between first and second degree murders.
First degree murder is a homicide committed with deliberately premeditated malice, or with extreme and wanton malice. Second degree murder is a lesser crime, in which a homicide is committed with malice but without deliberation or premeditation. The Columbia Encyclopedia, Sixth Edition.