Geberth’s Practical Homicide Investigation defines serial murder as two or more separate murders where an individual acting alone or with another, committed multiple homicides over a period of time with breaks between each murder event (2015). 

The FBI defines serial murder as the killing of three or more separate victims with an emotional cool down period between killings (2016). These cooldown periods can range from days, to weeks, to months or even years between victims (2016). During this emotional cool off, the perpetrator may reflect on what they did, such as dwelling on pleasure he/she felt with the horrifying treatment and murder of another human (2016). The individual may contemplate on the effectiveness of their approach to their victim, and if they achieved the ends desired (2016).

Bachman, R., & Alvarez, A. (2016). Violence: The Enduring Problem. SAGE Publications. 

Geberth, V. J. (2015). Practical Homicide Investigation: Tactics, Procedures, and Forensic Techniques, Fifth Edition. Taylor & Francis.