In a perfect world we’d all wait for the investigation to conclude and present it’s results.
We don’t live in a perfect world. We’ve already had an eyewitness account claiming an execution, one that produced multiple nights of rioting, get proven false by an autopsy.
Other claims (Brown standing with his hands up in surrender) are easy to call into question based on the picture of Brown’s body, post shooting.
This is a battle already being waged in the court of public opinion. Which is the real world. We better darn well engage, and engage early and forcefully, because the narrative put forward by the other side will become fixed if we don’t.
The problem, of course, is that the way things are in the real world now, both narratives become "fixed" by those who believe them. Short of a video of the shooting itself, the competing narratives are fixed. I don't think there is a fact that could come out that would convince those who believe in the "Brown standing with his hands up in surrender" narrative that this was a justified shooting. Likewise, I don't think there is any fact that could convince those who think that Brown attacked Wilson and was bum-rushing him when Wilson fired that the shooting was unjustified.
Not that I have a solution to this problem (short of "everybody calm down and wait until the investigation is complete," which is obviously unrealistic). Just pointing it out.