Is it really necessary to kill killers?

It's too late now. Serial killer Tommy Lynn Sells was put to death. I ran across a missing person from the 80's I think it was, she was from an area where Tommy had killed another person. Still just a missing person, no one knows if she's alive or dead. I immediately suspected it could have been one of his victims, but they killed him. If he were alive, he would have confessed to it if he had done it. I think I'm the only one that suspects it's one of his victims, if he were still alive I would go to the police or whoever I need to so they could investigate. No point now though. Probably a case that will always be left hanging