The situation wasn't that black/white. The cop was negligent and the situation could have been handled better. A person with a knife surrounded by many others isnt likely to instantly kill someone and could have been restrained differently. We also havent seen the full footage yet and dont know the who the aggressors where in the situation. For all we know the girl with the knife could have been the person defending herself from attackers (I believe she is the one who called the police). I'll wait for more details to come out about the situation to say anything definitive.
Cops should be held accountable. That's all Lebron is saying. He's the next to stand trial.