I know! Lets use a legal dictionary!
http://dictionary.law.com/Default.aspx?selected=1303Quote:
murder
n. the killing of a human being by a sane person, with intent, malice aforethought (prior intention to kill the particular victim or anyone who gets in the way) and with no legal excuse or authority. In those clear circumstances, this is first degree murder. By statute, many states consider a killing in which there is torture, movement of the person before the killing (kidnapping) or the death of a police officer or prison guard, or it was as an incident to another crime (as during a hold-up or rape), to be first degree murder, with or without premeditation and with malice presumed. Second degree murder is such a killing without premeditation, as in the heat of passion or in a sudden quarrel or fight. Malice in second degree murder may be implied from a death due to the reckless lack of concern for the life of others (such as firing a gun into a crowd or bashing someone with any deadly weapon). Depending on the circumstances and state laws, murder in the first or second degree may be chargeable to a person who did not actually kill, but was involved in a crime with a partner who actually did the killing or someone died as the result of the crime. Example: In a liquor store stick-up in which the clerk shoots back at the hold-up man and kills a bystander, the armed robber can be convicted of at least second degree murder. A charge of murder requires that the victim must die within a year of the attack. Death of an unborn child who is "quick" (fetus is moving) can be murder, provided there was premeditation, malice and no legal authority. Thus, abortion is not murder under the law. Example: Jack Violent shoots his pregnant girlfriend, killing the fetus. Manslaughter, both voluntary and involuntary, lacks the element of malice aforethought.
See also: first degree murder homicide malice aforethought manslaughter premeditation second degree murder