Iirc the George Zimmerman stuff is in front of a Federal Grand Jury now. There were a couple threads on it a few weeks back.
Given the overloading of evidence in favor of Wilson and against Brown, the DoJ would have to be insane to go after Wilson. The outflowing of public support (donations to a legal defense fund) would be significant, as would the poisoning of relationships between DoJ and state/local law enforcement.
I have occasionally wondered whether American Soldiers would ever get fed up with defending this country and our way of life, such as it is.
Similarly, I wonder whether LEOs would ever get fed up with defending or working In some of these communities. What would motivate a guy like Wilson to get up every day and go into a town like Ferguson and defend it? What would motivate an upstanding merchant to make that town his place of business?