Um... just... wow.
This is the situation you train for, but never ever want to wind up in. What's impressive is that this guy kept his cool and waited as long as he did. Sometimes, you read stories like this, and the victim draws while he's still got a gun pointed at his face. This is a good way to get yourself killed. It takes much less time for the Bad Guy to compress his trigger than it does for you to draw, aim, and fire.
To read the description, this robber never took his weapon off a victim, and never took his eyes off the armed victim long enough for him to draw. When he finally took his shot, it was still a terribly risky situation. But he was finally in a position where he knew he did not have much time left, and took the best opportunity he was given--the brief moment the robber looked away into the alley. I would have been very tempted to turn and shoot on the move when the robber fired at the cashier's desk. At that moment, the safest assumption is, "He's just shot my co-worker, there's no reason I'm not going to be next." I'd rather take my chances than take an easy one in the back just standing there. That this guy waited it out is impressive, and may have been the better decision. It's also impressive that, once the robber was down and the police on their way, he consciously kept his finger indexed on his pistol's frame, and had the sense to remind his partner to do the same with his shotgun. This is exactly how you're supposed to think and act.
What amazes me is this asshole actually found an attorney to take up his civil case. That's just a fucking joke. I agree with the principle that everyone is entitled to the best possible legal defense. But to take up this plaintiff's case, you really have to be a special kind of asshole.