I want to put a f/cking bullet in his brain and toss him into an unmarked ditch. there's no pain in that.
You are still providing no value to that action beyond your own self-gratification. You're not really making a strong argument for being better.
Now, I don't mean to actually compare you to the refuse of humanity that is the topic of discussion. I don't know you well enough to know for sure, but odds are good that you're at least a decent human being. What I'm trying to point out is that there is a core reasoning flaw in your argument that's also underlined in his actions. He thought he was better. He did what he did to his victims because he wanted to, and because he either couldn't think of a reason not to, or ignored it, because he thought he was better.
Part of actually being better is not causing harm to others for reasons that go no further than your own whim. You should have actual reason to even suggest putting someone down. Otherwise, you aren't actually better. Just lacking in depravity. Which, you know, is a good quality to lack, but claiming to be better on that account is a bit like claiming to be better than a cripple. Being better is going beyond your nature and doing things that are constructive. That's what civilized world is built on. And sometimes, maintaining that civility means letting someone live, when they really don't deserve to.
That said, if he trips in the common yard and falls on a shiv five times, well, these things happen. There is reason enough to maintain a degree of order in prisons, but I don't really expect any of the guards to put their lives under any additional risk to shield his.