Wait for him to make the first aggressive move towards the police. That's why I keep saying, have a set rules of engagement. Not a policy that isn't know to the public and up for review behind closed doors. Something black and white so we can look at the video and say "did he take a shot at the police" fine, the kill was justified. But as of right now, everything is gray and the police are allowed to fall back on "I thought he was going to act aggressive".
As of right now, people are completely fine with killing a civilian based on a bunch of maybes. Maybe he was going to do harm, maybe he was having a bad day, maybe he wasn't right in the head, maybe he was deaf and didn't hear the commands.
The police never tried to figure any of those maybe out, they yelled at him and when they didn't like the results, they shot.