It doesn’t matter if he is a convicted murderer. He was the intended victim and he had every right to refuse to be a victim and defend himself in an effective and overwhelming manner.
According to the story they kept trying to get up when he told them to stay down. The goal is to beat your opponent into submission in order to win and he did this. Unfortunately it took this much force into order to achieve that. This tells you just how out of control these thugettes were.
Would you rather him be the victim?
There are always a few folks who seem to think that a person who defends himself against a sudden, unprovoked, violent attack MUST respond rationally, logically, and coolly, and they are horrified if the person attacked fails to do that. Almost without exception, such people have never suffered a sudden, unprovoked, violent attack themselves.