OK, let's wait until the full investigation is completed. It's my opinion - assuming I'm allowed to have one - the conclusion will be the same. This officer fought back against someone who was armed and attempted to shoot him. The officer lived, his adversary didn't. I'll give this officer the benefit of the doubt, but it appears you won't.
How do you know what happened, or who fought who? You know nothing.
Heck I'll give him the benefit of the doubt, that's not your position however. You already had figured everything out and came to the "end of story" conclusion, when the only evidence available was a dead non-suspect with two holes in his back, and a flying gun with no fingerprints or chain of ownership.
You sound like ex-LEO, I hope you're not current LEO. It would be troubling to know that you're on the street given your bias and approach to critical thinking.
If nothing else it's s***ty and unprofessional police work when non-suspects wind up dead during the course of the investigation.