If Brown was fleeing an officer, who has warned him to stop, the officer would be justified even if he shot him in the back. Not saying Brown was shot in the back, but even if he was, the officer would have been justified. The first autopsy said there were no shots in the back.
I don’t know about Missouri, but in Tennessee if someone commits a crime and a citizen or a cop tries to apprehend them, they are authorized to use whatever force is necessary to bring them to justice, including deadly force.
That doesn’t mean that you can summarily execute someone, without warning while trying to apprehend. But it does mean that if a perp robs a store or assaults a cop and then runs, and that cop issues a warning to freeze, that cop would have the right to shoot to stop the fleeing suspect.
What?
Not so, at least not since 1985. That was when the US Supreme Court ruled that deadly force "may not be used unless necessary to prevent the escape and the officer has probable cause to believe that the suspect poses a significant threat of death or serious bodily harm to the officer or others."
So it seems that a cop (or a citizen) had better be able to make a very strong argument that the suspect poses a significant threat. Shooting simply to prevent an escape isn't enough.
You are wrong about the law in Tennessee. It’s not nearly as simple as you imply. If fact, there is a famous U.S. Supreme Court case about shooting a fleeing suspect involving the state of Tennessee. I suggest you read it
http://caselaw.lp.findlaw.com/scripts/getcase.pl?court=US&vol=471&invol=1