When a police officer says the evidence speaks for itself, what he really means is why don't you help me fill in the gaps, the truth is the evidence is not obvious and the evidence doesn't speak for itself. They want you to speak for the evidence. They want you to give evidence against yourself. You should actually leave the room and not speak. What the police officer is really doing here is he's trying to convince you that he has all of this evidence against you to build this case against you and that you talking to him doesn't really matter. The actual truth is he probably doesn't have any evidence against you and he needs you to fill in the gaps. You know what the cop would do if he actually had all of the evidence against you? He would walk in and say, "Turn around. Put your hands behind your back. You're under arrest.