I get that Avery might have been a perpetually petty criminal, but that wouldn’t relevant in the trial in question for the circumstances that this happened under. In this case, Avery did not commit a crime worth taking a life over. Once he started running, you let him go.
Attacking a man with a shotgun and punching him in the face while trying to wrest the gun away from him is not a crime worth taking a life over?
So if someone punches you in the face and tries to take a shotgun away from you, I suppose you will conclude that he hasn't committed a crime worth the trouble for you to pull a trigger?
That's assuming McMichael actually pulled the trigger rather than that idiot pulling the gun forward against McMichael's hand thereby activating the trigger.