Nate Silver laying down some statistics
It’s Incredibly Rare For A Grand Jury To Do What Ferguson’s Just Did
Former New York state Chief Judge Sol Wachtler famously remarked that a prosecutor could persuade a grand jury to “indict a ham sandwich.” The data suggests he was barely exaggerating: 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.