Can someone explain a scene from "The Dark Knight"?

The female cop doesn't blame Batman. She just despises him and gets angry when Batman asks for a couple minutes in the crime scene before her people mess it up. She gets angry that he said her people mess it up so she got all bitchy. Batman didn't set it up, Joker did. Also i think it is totally BS how Batman gets the fingerprint from the shattered bullet in the wall. There is no way that is possible.