According to the Bureau of Justice Statistics, U.S. attorneys prosecuted 162,000 federal cases in 2010, the most recent year for which we have data. Grand juries declined to return an indictment in 11 of them.
Wilson’s case was heard in state court, not federal, so the numbers aren’t directly comparable.... Still, legal experts agree that, at any level, it is extremely rare for prosecutors to fail to win an indictment.
Which of course means that prosecutors go before grand juries with their minds made up, which arbitrarily bars other minds from the decision-making process. That's why so many residents of Ferguson will interpret the grand jury's decision as nakedly illegitimate, which, further, is why a jury trial in the Brown case was essential. The shooting required a full, public and transparent hearing. Only that would have kept the peace.