Verified by 
During the past 40 years, several different definitions of serial murder have been used by law enforcement officials, clinicians, academicians, and researchers. While these definitions normally share common elements, they differ on specific requirements such as the number of murders required, the types of motivation, and the temporal aspects of the murders.
Typically, definitions of serial murder specify a certain number of murders, varying from 2 to 10 victims. This quantitative requirement distinguishes a serial murder scenario from other categories of murder, especially single homicide, which is by far the most common act of murder.
Most of the definitions also require a period of time between the murders. This pause or break between killings is necessary to distinguish between a mass murder, which is a one-time event, and a serial murder, which has multiple incidents.
More specifically, serial murder requires a temporal separation between the different murders which is variably described as separate occasions, the cooling-off period, or the emotional cooling-off period. I use the term cooling-off period to refer to the temporal requirement.
Perhaps due to the debate among professionals over the exact definition of serial murder, the government actually attempted to formalize it through legislation on one occasion. In 1998, a federal law was passed by the United States Congress, titled the Protection of Children from Sexual Predator Act of 1998 (Title 18, United States Code, Chapter 51, Section 1111). This law includes the following definition of serial killings:
The term ‘serial killings’ means 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.
This federal law provides a definition of serial murder but it is limited in its usefulness because it was only designed to establish criteria for when the FBI could assist local law enforcement agencies with their investigation of serial homicide cases.
At a symposium on serial homicide in 2005, the FBI reduced the minimum number of victims from three to two in its own definition of serial murder (1). The FBI did this for its own purposes and to satisfy its own needs—that is, to afford itself greater flexibility and breadth in determining when and how to pursue potential serial murder cases.
In addition to lowering the minimum number of murder victims in 2005, the FBI also eliminated the cooling-off period from its list of required serial homicide criteria. Similar to the rationale it used in lowering the number of victims, the FBI argued that the cooling-off period is not a useful requirement for the purposes of a criminal investigation.
However, from a social-psychological perspective, the emotional cooling-off period between murders is a key behavioral characteristic that distinguishes serial killers from all other types of murderers. Therefore, I contend that it is vital to the definition of serial murder in terms of understanding the pathological needs and criminal psychology of the perpetrator.
The cooling-off period is important because it constitutes a time-out from murder for a serial killer. During the cooling-off period between murders, a serial killer disappears from the public eye and resumes his/her seemingly normal routine and life. Incredibly, the life of a serial killer during the cooling-off period, particularly if he/she is a psychopathic killer like Ted Bundy or Gary Ridgway—that is, pathologically devoid of emotion or empathy—may appear completely normal to the unsuspecting observer.
Serial predators reemerge from a cooling-off period to strike again when the urge to kill becomes overwhelming to them. A serial killer may not even understand his/her compulsion to kill but knows that it is both undeniable and uncontrollable when the urge arises.
The cooling-off period is to a serial killer what coming down from a narcotic high is to a drug addict. It is a time of rest and re-composure. The cooling-off period is only a temporary time-out, however. Soon enough, the serial killer will need another victim, just as the heroin addict will eventually need another fix or the alcoholic will need another drink to calm their cravings.
The cooling-off period between murders is highly subjective and unpredictable. Its duration varies from one serial killer to another. The length of the cooling-off period can also vary between murders committed by the same serial killer. The duration can be from days or weeks to months and in rare instances, even years.
For example, Dennis Rader, or BTK, confessed to 10 murders that he committed over a span of nearly 20 years (1974-1991) after he was captured in 2005. In between his murders, Rader lived a remarkably normal-looking outward life with a wife and 2 children. He was perceived as a pillar of his community in Wichita, Kansas.
Inwardly, however, Rader was secretly satisfying his sexual needs and delaying his compulsion to kill for months and even years at a time through autoerotic fantasies in which he relived his murders with the aid of trophies taken from his victims such as articles of clothing, identification cards, and jewelry.
As a result of this practice, the length of the cooling-off period between Rader’s murders was highly variable and often lasted much longer than other serial killers. His ability to control his compulsive need to kill for years at a time through autoerotic fantasy is highly unusual for serial killers.
To summarize, the cooling-off period between murders is subjective and varies by the serial killer but it is a unique and distinctive behavioral characteristic that distinguishes the serial killer from all other types of murderers. Although it may not be critical to the FBI for their investigative purposes, the cooling-off period is nonetheless essential to criminologists’ understanding of serial murder in terms of the pathological needs, motives, fantasies, and psychological makeup of the perpetrator.
References
1) Morton, R.J. 2005. Serial Murder: Multi-Disciplinary Perspectives for Investigators. National Center for the Analysis of Violent Crime. Washington, D.C.: U.S. Department of Justice. Retrieved http://www.fbi.gov/stats-services/publications/serial-murder
