Actually it's not the cops that have to prove that we are guilty, it's the prosecutors. The Police only gather evidence and when they have enough, that warrants an arrest. From that point on, it's all up to the prosecutors.
But no, I disagree thannine, we are innocent until proven guilty with a fair trial which still exists in the U.S. Justice System. Even if the person is despicable and obviously guilty, they still deserve their right to a trial.