they're very often not able to control their compulsions. the cooling-off period usually gets shorter and shorter and shorter. the thrill is gone. they have to get out there. they have to kill again. ♪ gagliano: these homicidal maniacs, they think they're smarter than the rest of us, and they think that they're going to pull off the perfect crime, and it doesn't exist. the arrogance was part of his downfall. hatteberg: we're not getting any communication from the police departments. something is happening. something is going on. woman: this guy? this is the killer? so i finally looked at him and said, "come on, just tell us who you are." and he said, "i'm btk." btk had killed seven people, including two children. he was taunting law enforcement with clues, but police were no closer to discovering his identity. although he left his dna at two murder scenes,