In all seriousness, he should have whatever criminal penalty (as long as it's constitutional) that the state administers for such a crime, so long as he receives a fair non politicized trial.
We live in a nation of laws.
That doesn't mean the world isn't a better place for it. You can commit a crime that benefits society, and it should still be a crime. If you burn down a bank, and everyone's debt records that work with that bank are destroyed, you've done a good thing. You should go to jail for arson, but you are a hero and that is your sacrifice.
If someone who know is a child abuser, and you show up and beat the living fuck out of them and put the fear of god into them... you should go to jail for assault. But you did a good thing.
The law is the not the harbinger of morality. In fact the law is often on the opposite side of morality, and even when it's not, there's always plenty of cracks to fall through.
Civil criminal action against evil works to counter evil when evil finds a way to flourish between the laws, or via an actually take over of the laws themselves (i.e. authoritarianism).
Charlie Kirk dying was a beautiful thing. If you think it wasn't, it's because you romanticize that monster. If you find yourself mourning him, it can be for several reasons. You either starting thinking of him fondly before your morality and conscience fully developed in your brain because you were young, and now you find it difficult to reexamine those beliefs. Or, you could be a pure sociopath that simply is incapable of feeling actual sympathy, and you had just put him on a pedestal. Or you lack the emotional intelligence to see how many people's lives he effected badly, and/or have so much insecurity you give your loyalty to anyone who tells you you're special and better than others.