it was the tangible reminder that there was a killer out there and that at some level the police thought he might be coming to see me. >> just what was it that drove dennis rader to bind, torture and kill so many innocent people? >> factor "x" is probably -- >> in his jailhouse interview, rader blamed his murder spree on that mysterious force he has always claimed was way beyond his control, factor "x." >> something that i used it, i actually think of maybe possessed with demons, i was dropped on my head when i was a kid. talked to some theological christian people and some of the people are really strong. they actually think, well, there's demons within you, and got into you. that's the only thing i can figure out. i haven't, you know -- something drove me to do this. normal people don't do it. >> you can't stop it? >> i can't stop it. it's just -- it controls me.