The whole thing about the gun being pointed at the guys head for one thing. When you read the articles in the papers about that night you'll see the cop said he was going to another call when he saw them punching and kicking the guy, so if they were beating him up and ran when the cop got there, then when did they have time to pull out a gun and point it at his head? The cop would have immediately drawn his gun and made get on the ground- running would only cause them to be shot for not putting it down because that's an endangerment to his life in the eyes of the law