I also don't know how a D.A. would "flub" a grand jury proceeding. If there were reason to believe the police had purposely made a slipshod investigation to cover up misconduct, and the district attorney had conspired in it, the state attorney general's office could make its own investigation, and even the U.S. Justice Dept. might get involved. Police officials who pull stunts like that are asking to end up in prison.