But he said he did see a police officer get out of the patrol car and start walking briskly while firing on Mr. Brown as he fled.

What happened next could be what the case turns on. Several witnesses have told investigators that Mr. Brown stopped and turned around with his arms up.

This article is a summary of witness testimony. Everything mentioned in the article agrees that Wilson shot at Brown as Brown was retreating. Why is it only what happens next that matters? Isn't shooting at a retreating person in defiance of self defense?

Also:

The accounts of what witnesses have told law enforcement officials come from some of those witnesses themselves, law enforcement authorities and others in Ferguson.

Many of them spoke on the condition of anonymity because they did not want to be identified discussing a continuing investigation.

So we don't know which accounts come from law enforcement (which is to say Wilson, since he was the only officer at the scene when the shooting took place), and which are relays of interviews conducted by local law enforcement, etc. None of the named witnesses say that Brown "charged" Wilson.