Murder is defined as the willful, intentional killing of another person(s). There are three distinct types of murder: mass murder, spree murder, and serial murder.

Mass murderers kill four or more people at one consecutive moment. Usually, a mass murderer is killed at the scene of the crime. An example of mass murder would be the 1995 Oklahoma City bombing committed by Timothy McVeigh. McVeigh detonated a bomb inside of a truck in front of the Alfred P. Murray Federal Building. The explosion killed 168 people, including nineteen children, and injured 680.

Spree killers murder two or more people, but at multiple locations. There is no cooling-off period when it comes to spree murders; this is why they are considered a single even and what distinguishes them from serial murders. An example of a spree killer is Charles Whitman. On August 1, 1966, Whitman killed his wife and mother at their home and then went to the University of Texas campus. At the campus, he shot 46 people, 14 of which died. He was killed by the police at the scene. Whitman would be considered both a mass murderer and a spree murderer.

Serial killers murder three or more victims on separate occasions. Serial killers usually plan out their murders with victims in mind. They also have a cooling-off period between their murders. Serial killers typically have a signature that makes their crimes identifiable. Ted Buddy is an example of a serial killer. Ted Buddy murdered 30 women between 1974 and 1978. He would wear a sling or cast and pretend to be injured and struggling with groceries. He would ask the victims to help him load his car; as the victim leaned into his car, he would strike them over the head; he would then rape and murder them.