Serial killers have long been a serious problem in the United States. We don't know why they kill humans, but many people are trying to understand why. A serial killer is a person who has killed three or more people in the space of a month. There is also a period of time between murders known as the "cooling off period". According to the Federal Bureau of Investigation, there have been approximately four hundred serial killers in the United States over the past century. The number of these killers has increased over the past thirty years, and approximately eighty percent of them have emerged since 1950. The term "serial killer" was coined in the mid-1970s by a man named Robert Ressler, former director of the Federal Bureau of Investigation's Violent Criminal Apprehension Program. "He chose 'serial' because the English police called these types of murders 'serial crimes' and because of the serial films he grew up watching." (Freeman). Before this term was created, these murders were known as mass murder crimes. Serial killers can be action-focused, killing quickly, or process-focused, killing slowly and torturing their victims. There are two types of serial killers. Visionary serial killers who kill people because they hear voices or have visions that direct them to do so. Then there are the murderous missionaries, who believe they are trying to get rid of a particular group of people. Within these two groups of serial killers there can be four different types of serial killers. The serial killers of lust, the serial killers of thrill, the serial killers of gain and the serial killers seeking power. Lust killers get sexual pleasure from killing, thrill killers get joy from it, killers gain killing b...... middle of paper ......who most likely had some kind of problem infantile such as divorce or the absence of a parent. They may think they are doing the world a favor, or seeking people's power, or simply taking pleasure in killing. As for why serial killers have increased over the past thirty years, there is no certain answer, but hopefully it will stop increasing soon and decrease instead. Works Cited Freeman, Shanna. "How things work "How serial killers work" "How things work. Network. May 22, 2014. Hickey, Eric W. “Serial Killer: Defining Serial Murder.” Serial killers. Network. May 20, 2014.Preston, Douglas J. and Lincoln Child. Still life with crows. New York: Warner, 2003. Print.Schlesinger, Louis B. “Serial Murders Are Really on the Rise.” Serial murders are really on the rise (2001). Web."Serial Killer." Wikipedia. Wikimedia Foundation. Network. May 22 2014.