Well he was unarmed and outside of his vehicle when he was shot according to reports.There is no evidence that he lacked justification for shooting him, either. There is no way to know. The video is unavailable to the public and will probably remain so until November.
The only way I can see this as a legit shoot as if the video shows the deaf guy going for the officer's gun.
Was this guy Jason Bourne or something?
If not, then I don't see any other feasible way this unarmed deaf guy, outside of his vehicle was a threat to the officer at all.
You can do pepper spray or tazer if you have it to someone not responding or not acting right. Also, officer's are trained in hand to hand actions as well.
So is the officer claiming the deaf guy went for his gun? If not, then its going to be hard for a video to prove to me killing this guy was the right move.