I imagine the scenarios where a person could be shot through the front part of the head and into the clavicle from a distance (no powder burns on body). He could be in the act of falling or charging. It would be very difficult if Brown was laying flat or on his knees. And if he was falling it would be a tough shot too.
The other thing is, if I am a murderous cop, and two suspects have their arms up saying dont shoot, why didnt I kill both of them? Why leave one alive to dispute my story? I agree that cops words have too much pull in our system, but as stated before, even if the officer was in the wrong, shooting someone that fits the exact description (from head to toe) of someone who just forcibly robbed a store, your co-robber's version of events probably wont hold up in court.
And even if I do not have a sense of ownership in my neighborhood, you can be sure if I protest it will be in the neighborhood of the perpetrator. Instead of destroying random stores, destroy the cops house...