BTK was the undercover name chosen by Dennis Rader which stood for "bind, torture, kill".  BTK went on a 30 year killing spree from 1974 to 1991, killing 10 people.  Finally, he was caught and arrested in 2005, and sentenced to life in prison.  Although his crimes were sadistic, vicious, and psychopathic, he got away with it for so long because he seemed like a  normal person, one of us.