How could the officer know he was unarmed? He had just committed a robbery.
Officers are trained to shoot at the body mass, the shots to the arm were probably misses.
There is a massive difference between shooting at a target on the range and facing a charging guy intent on doing you harm. Shooting to wound aiming at the legs etc, is O.K. For Hollywood but will get you dead in real life.
The officer would continue to fire until the guy dropped. The fact that he did not empty his clip shows restraint.
It might be valid if the alleged perp had a weapon showing do you not think?
Seriously, so all you have to do is lurch towards a LEO in the US with arms outstretched and empty and get shot down at a distance with 6 rounds most of them missing the "centre mass?" I'm not buying it.
At best he (the cop) was incompetent, at worst, well, the jury will probably be out for ever on this one.