Self defense is a situation where you almost never have total certainty.
You don't need total certainty. In this case, the gun was inside the car and
presumably the shooting victim was not reaching for it. It doesn't appear the victim was shot in the vehicle, but he had been inside the vehicle at some point. So if he had been getting it, he'd have it. Even given all this, I still maintain, arguing over this isn't the most important part of what happened. The police stood by after reasonably knowing he had no gun for minutes without helping him to survive. That kind of mentality is too present in the police. I just see it too much. They have to treat life and death situations with urgency, even if the victim is an apparent criminal. So they can easily verify his claim he wasn't going for the gun by looking in the car where he said it was. Or simply inspect him. Then apply first aid.