I think, in this case, an execution similar to the Zamboni machine scene in "Deadpool" would work rather nicely.
I know that sounds terribly uncivilized but one of the reasons things like this happen is the total lack of consequences for this kind of behavior. Being overly civilized results in the worst in our society becoming totally uncivilized while everyone else walks around like the citizens of "Greater San Angeles", sheeple waiting for the slaughter and then cooperating in their own slaughter.