And that's where justice isn't served.
Let the scumbag live, but make it awful. Let him pay for every life he took or ruined.
If he goes to prison, he'll be put in a private cell to rot and be forgotten about. Literally the entire purpose of what he set out to achieve will be cancelled out, because he wanted to be known and talked about and celebrated and none of those things will happen. He won't be a martyr or an inspiration or a symbol, he'll be a sad little man living the most pointless life until his unremarked and unnoticed death many purposeless years in the future.
That's the right course of action, not publicly parading his head on a stick to polarise and publicise extremes.