There exists the problem of wrongful conviction, particularly when the victim is a child, and more susceptible to outside influence. That aside.

If there exists clear proof (DNA, video, etc) then the death penalty seems the only long term solution that works. Long prison terms have a magical way of becoming shorter as time goes by. And then we have another victim.

When one of these guys is arrested, it is rare indeed, to hear that this is their first run-in with the law. They have usually done this several times before that the legal system was aware of.

Death penalty