Kyle had as much a right as anyone else (i.e. the rioters) to be there. The prosecutor himself admitted that the "protestors" were causing property damage and arson.
Additionally, rioters brought guns as well.
Mr. Grosskreutz is an example.
“It wasn’t until you pointed your gun at him, advanced on him with your gun — now your hands down, pointed at him — that he fired, right?” Mr. Chirafisi said.
“Correct,” Mr. Grosskreutz said.
Kyle didn't do anything illegal. You can comment on his negligence, but not his legality.