For instance, if Mike Brown had started an incident but then stopped resisting and was shot after he stopped resisting submitting to the arrest, the cop murdered him. It's all a question of context that the undisputed facts fall under.
This is actually interesting from a self-defense perspective. People who actually know self-defense laws know that you're only allowed to continue fighting until the person is no longer a threat. Even if they start the fight, if they back down, you can't just keep kicking the shit out of them and call it self-defense. This opens up worlds of gray areas for courts to sort out though. For instance, say somebody sucker punches you, then backs off and says "Hey, man. I don't want to fight." What do you do?
HOWEVER, if you believe your life is in danger, you can respond with lethal force (how Zimmerman got off). And ultimately, dead men tell no tales. I've raised the point before that any person carrying a gun would legitimately have their life "in danger" any time they got into a physical altercation because "he went for my gun" is always in play.
This is why in concealed carry courses, they teach you to avoid conflict and to back down in any argument you ever get into while carrying...because you have a crap ton of responsbility strapped to your body (where Zimmerman was wrong).
Obviously, police officers can't exactly abide by these same rules. Does that mean our law enforcement should stop carrying firearms? Of course not. That's crazy. But it also takes a special kind of crazy to attack and go after somebody's gun. There's just so many factors at play here beyond "White cop shoots unarmed black teen."
My opinion...regardless of who it is...flip-flop their skin color...I don't care, if the evidence supports a significant attack against the police officer, then the action was justified. I have no qualms with law enforcement killing anybody who punches them in the face and tries to grab their gun. Just prove to me that's what actually happened.