The reason most civilized nations have removed the death penalty is that even in modern criminal cases, at least one in five convicted persons are innocent.

If you lock someone up, there is the possibility of releasing them and providing them with an income to say sorry for taking most of their life away. If you execute them, nothing can be done to make amends - it is a final and irreversible step.

I cannot even imagine the kind of kangaroo justice that would be encouraged by attempting to go after anyone involved in this current state of affairs. If we get things wrong 20% of the time with a stable society, how well are we going to fare on establishing guilt when we're trying to quickly process tens of thousands of stormtrooper cosplayers? Yes, they're probably horrible, horrible people, but I think extreme repercussions should be reserved for ringleaders and people in a decision making capacity. Even then, we should stop short of killing them.

I am fairly sure the people on the ground acting out will have the rest of their lives to process the trauma they've inflicted on themselves, their communities and their victims - and many of them won't be able to come to grips with it in this lifetime.