I am not saying he should have at all but once he was going for a lethal shot, why wouldn't he take a head shot. Center mass looked difficult at that angle but a trained person could make that head shot. Why wasn't there shouting of "stop, get back or I will shoot - do not come any further, do you hear me?" didn't seem like any of that.

I understand lethal force if a mob is busting into an unauthorized area but it seems the warnings would be given.