He made the choice to join a cult... the killer doesn’t get a pass for that anymore than he would get a pass for joining a street gang.
Lie down with dogs - wake up with fleas...
I am not at all suggesting that he get a pass.
I love my dog. If my dog got rabies, I would shoot her without hesitation. I wouldn't do it to punish her or to make an example of her to other dogs. I would do it because a rabid dog has to be put down immediately before she bites anyone. There is no way to rehabilitate a rabid dog.
How she got rabies would be irrelevant to the issue of whether or not she needed to be put down. I would still want to know how she got rabies though, to try and prevent or at least reduce the continued spread of rabies in the area.
Pretty much the same analysis applies to rabid Muslim killers. He needs to be shot, regardless of how he became a rabid Muslim killer. The only difference between a rabid Muslim killer and my rabid dog is that, unlike my rabid dog, the Muslim killer needs to be punished too. It is still important to find out how he ended up that way though, to try and prevent or at least reduce the continued spread of rabid Muslim killers.