...and the next victim that they hit hard enough to kill or put into a coma... it is called prevention. You shoot one close enough you can argue that you thought they were re-grouping for another go. Better judged by 12 than carried by 6.
I agree that he could have shot them to stop the attack. But once the attack ended it is not a legal use of a firearm to shoot people as they are running away.
Even if they are black.
Am I the only one here who give a crap about the rules?