It is standard procedure to withhold information during an active investigation. As a matter of fact, as was posited by the State Trooper in charge of the investigation, nothing should have been released until the investigation was complete.
Sounds like the local police chief panicked, and with good reason, and released some information with the idea it might keep riots from happening in his city.
My personal opinion is that this whole Brown affair has been stage managed from the gitgo by race baiting agitators trying to turn a tragedy into political and finical gain for themselves.
They were using the fact that the police have strict rules preventing disclosure of evidence and taking advantage of this silence to gain control of the narrative of the case and try the police in the court of public opinion in such a damaging fashion that the true facts of the case would never make a dent in their false narrative.
I think the Chief put the word out that he was going public and it shocked the race baiters who were inciting and organizing the riots enough to force them to back down and call off the thugs to allow things to cool down.