Timing is everything. That was intentionally done. Anyone with common sense would know it was going to enrage people and cause more riots. They could have released before or during the trial. The excuse the chief gave was BS. That was a coordinated attempt to bridge that incident with the shooting.
No, in fact, that is not common sense. It was done at the request of the media and the public when it was discovered that Brown was a criminal.
In fact, the release of the video was perfectly timed to tamp down violence. Despite what you think, the decent folk of this town, when seeing that brown was just another petty criminal, would actually stop to think about what they were protesting and would likely (at least the intelligent ones) pause or stop their protesting until such time as they had more information.
I realize you don't hold that high a regard for the black community, but it seems that many others do.
There is really only two things that anyone can say about this for certain. That no one (not even the police at the moment) has all the facts and that Brown is not an innocent kid who was the victim of racism.