SAN ANGELO, Texas —Multiple definitions of serial murder have been used by law enforcement and media over the years and while these definitions have shared common themes they have not agreed on the requirements so the question remained: What does it take to become a serial killer?

The majority of discrepancies have included the number of murders involved, the types of motivation, and the duration over time of the murders, so in order to amend this, the FBI came together to develop a single definition for serial murder.

Attempts to define a serial killer began with the number of murders committed to distinguishing them from other categories of murder such as single, double, or triple murder. Additionally, it also required a period of time between the murders in order to distinguish between mass murder and serial murder.

It was concluded that a serial murderer required a separation between the different murders, which was described as a “cooling-off period” whereas a mass murderer was described as a number of murders occurring during the same incident in a singular location.

The first attempt to formalize a definition of serial murder through legislation occurred in 1998. This law, “Protection of Children from Sexual Predator Act of 1998”, defined serial killings as, “a series of three or more killings, not less than one of which was committed within the United States, having common characteristics such as to suggest the reasonable possibility that the crimes were committed by the same actor or actors.

The FBI never intended for this to become the generic definition and it was only utilized in order to assist local law enforcement agencies with their investigation of serial murder cases.

The motivation of serial murders was also called into question in the search for a definition but it was decided that it would make it overly complex.

The factors they did agree should be included in the definition were:

  • One or more offenders
  • Two or more murdered victims
  • Incidents should be occurring in separate events, at different times
  • The time period between murders separates serial murder from mass murder.

These combined created the following definition from the FBI: Serial Murder: The unlawful killing of two or more victims by the same offender(s), in separate events, officially defining what it takes to become a serial killer.