One of the issues raised by the community leaders and protestors was their distrust of the local authorities. The additional autopsy by the DOJ and their promise to keep an eye on the investigation addresses those concerns.
Hey, it works both ways. It seems to me that one of the main things that has slowed down the Brown supporters/police bashers is the fact that the autopsy results show he was not shot in the back. This is important for many obvious reasons, not the least of which is that it immediately calls into question the accuracy of the friend's description of what occurred.
Can you imagine what would have happened had only the local autopsy been done, showing no shots in the back? The rioters would be claiming that it was faked, a cover-up. With DOJ doing one, with Baden doing one, and showing the same thing, it just gets us all past at least the one side-show issue.
And, as I say, it makes you question the friend's account, since he is evidently objectively proven wrong by this result. Holder going down there buttresses the fact of oversight from the outside, and removes just one more issue from the dispassionate and reasoned approach that must be taken to the evidence as it emerges.