You determined that the cop tried to physically stop him... by listening to the video? No, I don't hear that. You must have some awesome speakers.
Or did you mean physically stop him, by putting bullets into him? Yeah, I DEFINITELY heard that.
See: I've listened to the video too, and the distance between 'don't get that out' to 'don't get that out!' or whatever the exact words is really, really short. So, please; don't try to sell us on 'kept moving after being yelling at', because 1. he wasn't reaching for his gun, 2. the cop never saw the ACTUAL gun (just the imagined one), and 3. he executed the man for not following directions, when no other job in the US has similar abilities to execute members of the public for not following directions.
Members of the public who are not actually doing anything illegal at the time, and are carrying things they are legally entitled to carry, and not actually even pulling out the any of them in question at that very moment.