Factor X from Top 10 Things You Never Knew About The BTK Killer

In 1978 Dennis Rader sent his 2nd letter to KAKE (it is a television station in Wichita) telling about so-called “Factor X.” In the letter, he explained this factor is the reason why he and other serial killers (Jack The Ripper, Ted Bundy, etc.) commit murders. He said it was like a motivation for him.