“The FBI has estimated that there are at least five hundred serial killers currently at large and unidentified in this country.” [Norris: 19]
“At present the FBI estimates there are at least thirty-five serial killers on the loose and under investigation by the Bureau.” [Norris: 37]
In a 2005 ABC News story, they claimed, “According to criminologists, at any given time there are at least 25 to 100 active serial killers in the United States.” No source was cited.
Norris, Joel. Serial Killers. Doubleday, 1988.
Thomas, Pierre. “Serial Killer Profiles Often Inaccurate”, ABC News. http://abcnews.go.com/WNT/story?id=539371#.TubeYFYg-14 February 28, 2005.