Wow. Very interesting. If the police are saying that Brown was running away when Wilson started to shoot, I'm inclined to believe them.
If Brown attacked Wilson (he probably did), seriously injured Wilson (he probably did), and went for Wilson's gun (no idea), then I still think Wilson had reasonable cause to fire at a fleeing Brown (the "fleeing felon rule"). But, if Wilson was shooting at a fleeing Brown, it's also possible that Wilson shot Brown even as he tried to surrender.
I still think the cop likely walks based on the prior robbery, aggressive behavior, and autopsy results, but an indictment might at least be appropriate based on these facts, if true.
The two wounds to the head are hard to square up. Both would have killed Brown almost immediately, and the only way the cop could have hit the top of Brown's head with the trajectory of the bullet towards his chin is if (1) the cop was standing over him - nobody is saying that - or (2) Brown's head was inclined towards Wilson. That suggests Brown was moving towards Wilson, unless he was already falling forward dead from the shot to the eye, which would make the shot to the head extremely difficult.