Some countries limit the time you can spend in prison for this very reason, no matter what you did. For instance, Brazil sets it to 40 years total even if you killed 100 people.
And 40 years is like the max, for raping and killing it's more like 15-20, eg a deranged man who chopped of a tourist's head is released in a few years after serving 15, another man that raped and killed a minor is soon to be out as well after 22 years in prison.
I'm lucky that I had parents which gave me behavior patterns which do not make me kill or rape others.
And even if someone believes they are right, they are actually right just no in the moral and ethical sphere of a majority.
I don't like rape and in my world it's wrong. But that doesn't change their world view. And I don't kill him due to this because why would I be allowed to end the life of someone else?
The best I can do is to remove this person from the society.
It's easy to kill and hard not to.
And in the worst case scenario I would kill someone who hurts or killed a close person (perhaps) but I would need to accept the consequences of it.