If the molester had been sentenced to death, I wouldn’t have any problem with the sentence being carried out.
However, when we sentence someone to confinement, then confine them, we have a moral duty to protect them while they’re in our custody.
I don’t think it’s moral to sentence someone to confinement, then rely on other criminals to kill them. If the man deserves the death penalty, we should take care of that ourselves. If he doesn’t, or, at least, if he’s not sentenced to death, then his God-given right to life remains in force.