a.. Wilson sees Brown and Johnson walking in the street and gets a little pissed off.
b.. As he drives by he orders them back onto the sidewalk, using profanity.
c.. Brown mouths off in response to the tone of the order.
d.. Wilson hears that and gets even more angry.
e.. He throws the truck into reverse and races backwards toward the pair.
f.. When the truck stops beside them, a now enraged Wilson throws the the door open with extreme force.
g.. It hits Brown, bounces back and smacks Wilson on the side of the head.
h.. The sudden pain triggers Wilson and all his residual self-restraint evaporates.
i.. He grabs Brown through the open window.
j.. Brown pulls free and starts to run away.
k.. Wilson jumps out into the street, aims at the running Brown, fires and misses.
l.. Brown hears the shot and realizes the danger he's in.
m.. He stops running suddenly (i.e. with a jerk), turns and raises his hands.
n.. Wilson is now fully in the grips of the adrenaline rage.
o.. Wilson aims for the head of the now-stationary Brown and continues firing until he goes down. This is supported by the autopsy diagram of the bullet wounds - if Brown had his hands up when shot, the diagram show a clear clustering of wounds at head level, slightly off to the left
p.. The fatal would in the crown of the Brown's head was probably the result either of Brown falling forward as a result of the earlier shots, or of him being shot while on the ground, as reported by eye witnesses.
This looks to me like a "vengeance execution" fueled by Wilson's steroid use (or something similar), compounded by a massive adrenaline rush that was triggered by the pain of being hit in the head by the police car door.
To put it bluntly, it looks to me as though Wilson got hit in the head by the door and then aimed for Brown's head in retribution.
But one thing is for sure, focusing on the subsequent police riots as "looting" is missing the point.