The most basic problem is that we will never know for certain what happened. Why? Because the Ferguson cruiser did not have a camera recording the incident. That's simply not credible. "Law" "enforcement" in Ferguson apparently has at its disposal tear gas, riot gear, armored vehicles and machine guns ...but not a dashcam. That's ridiculous. I remember a few years ago when my one-man police department in New Hampshire purchased a camera for its cruiser. It's about as cheap and basic a police expense as there is.
Last year, my meek mild-mannered mumsy office manager was pulled over by an angry small-town cop in breach of her Fourth Amendment rights. The state lost in court because the officer's artful narrative and the usual faked-up-after-the-fact incident report did not match the dashcam footage. Three years ago, I was pulled over by an unmarked vehicle in Vermont and (to put it mildly) erroneously ticketed. In court, I was withering about the department's policy of no dashcams for unmarked cars, and traffic cops driving around pretending to be James Bond but without the super-secret spy camera. The judge loathed me (as judges tend to), but I won that case. In 2014, when a police cruiser doesn't have a camera, it's a conscious choice. And it should be regarded as such.
http://www.steynonline.com/6524/cigars-but-not-close
In other words, given the bureaucratic incentives at play, it's more likely that the cop murdered the kid--as opposed to having good reason to kill him in self-defense.