Please note: this page is not a substitute for a lawyer and is meant only to inform, not to set guidelines or provide legal advice.
Murder is morally defined as the deliberate act of ending another living being's life, although the legal definition of murder may vary by type depending on the circumstances and the definition determined by the state. Murder is legally generally defined as the act of killing another human being with "malice aforethought", being the intent to kill or inflict bodily injury. Murder can happen as a result of protecting one's own life, and may be argued as self-defense, if the circumstances are applicable.
There are different degrees of murder, and to what constitutes the those degrees varies also by state. First degree murder is the most serious charge, and is usually assumed it occurred "with intent to kill", or premeditation. This means that it is usually argued that the individual contemplated the act before it occurred, with no restriction on the duration of the thought.
Second degree murder is usually defined as a killing that was intentional, not necessarily premeditated, but also not committed in a "heat of passion". Second degree murder can also include a murder by means of dangerous conduct or a lack of concern for human life.
Voluntary manslaughter is defined as an intentional kill in which the individual did not have any prior intent to kill; such as in the "heat of passion". This circumstance must be one in which a rational person would be driven to become emotional or mentally disturbed.
The rate at which members of a city or state are murdered is referred to as the "murder rate". Cities that demonstrate high annual murder rates can also be plagued by social disorders such as poverty, high drug trafficking and/or use, or gangs. Some cities have instituted laws and structural changes in an attempt to reduce the murder rate, such as increased law enforcement presence, and ban on private weapons possession.
A distinction is made, among murderers that have multiple victims, based on the time period of their killing: spree versus serial.
Spree killers, sometimes called mass murderers, kill multiple people in a single incident or closely spaced incidents. Examples would include Eric Harris and Dylan Klebold at Columbine High School, Charles Whitman at the University of Texas clock tower, a variety of workplace incidents, or, even though there was a political component, Timothy McVeigh's 1995 Oklahoma City bombing. Spree killings may end with the murderer's suicide (e.g., Harris and Klebold) or killing by police (e.g., Whitman); they conceivably could go onto serial killing, but the two types seem to take different personality types.
Serial killers are murderers that kill in multiple incidents over a prolonged period of time. They usually exhibit patterns in the choice of their victims or by a recurring trait or motive. Some of the most infamous serial killers of the twentieth century include the Zodiac, Ted Bundy, John Wayne Gacy, and the Son of Sam a.k.a. David Berkowitz.
Murders that occur en masse, as a part of a political movement, may be summarized as genocide or ethic cleansing, depending on the political or ideological means involved. A term often synonymous with the aforementioned is "holocaust", but this term has a connotation that usually is used in the context of "the holocaust", which occurred during World War II as a part of Hitler's campaign to destroy the Jewish population in Germany and parts of Europe.
Another type of murder is assassination, which is employed in order to affect some political, ideological, corporate, or economical gain. Assassination usually involves the murder of a key individual; often a high-ranking officer of an organization or a government, or someone who is able to control the "market forces" through policy setting or lobbying. Not all acts of assassination are performed by rational individuals, however. Some believe that by assassinating a key figure, they will change the world for the better in their view, or in the case of John Hinckley Jr, an attempt to "impress" actress Jodie Foster.
There also exist factions that may put the context of murder into the realm of "liberation", to imply a gain of freedom from oppressors. Such liberations may or may not be violent in their means, as it depends on the groups' motivations. One example of this was the Symbionese LIberation Army or SLA. This group was established around 1973, and was involved in the assassination of the superintendent of schools Dr. Marcus Foster in November of that year. The motivation behind Foster's murder was their objection to his "fascist" policies, as stated in a letter sent to the San Francisco Chronicle.