A non-indictment tosses the ball back to the Justice Department. U.S. Attorney General Eric Holder certainly has had a firm and visible handprint all over the Brown killing case. He quickly flooded Ferguson with teams of federal investigators in the aftermath of the killing, ordered an autopsy of Brown and made several high-profile appearances in Ferguson and St. Louis. He's also filed civil rights charges against nearly 400 cops during his tenure. That number far exceeds the number filed during the George W. Bush years. Holder certainly could make the case that Wilson abused his power in killing Brown under the cover of law, and that this violated several key civil rights statutes. This is the linchpin of federal prosecutions of local police officers. This was the rationale that federal prosecutors used in the Rodney King beating case to bring civil rights charges against the four LAPD officers who beat King. The crucial legal point was that they acted in an official capacity when they violated King's rights. But that's still a high bar to prove.
And the Justice Department time and again has made it clear that they are only a "backstop" to local prosecutors. This means that they rigidly adhere to the legal doctrine of separation of federal and state powers. The killing of Brown, as all potential criminal cases, was first and last a state matter, and the feds scrupulously defer to local authorities to bring charges. If state or county prosecutors won't bring charges or bungle the prosecution when they do, the Justice Department does not regard it as its responsibility to override the decision of local authorities not to retry or second guess a defendant's acquittal. There are two ironclad requisites for a federal prosecution of a police officer for the criminal use of deadly force. One is that there has to be solid proof that the officer acted either with racial animus or with reckless intent to cause malice to an individual. There appears to be no evidence that either was the case with Wilson.