The police proceural is a sub-genre of the mystery story which attempts to convincingly depict the activities of a police force as they investigate crimes. Unlike typical detective novels, which concentrate on one crime, police procedurals frequently show how police officers work to solve multiple crimes simultaneously. In contrast to the whodunit convention of having the criminal's identity concealed until the climax, in police procedurals, the perpetrator's identity is often known to the reader from the outset. Police procedurals depict a number of police-related topics such as forensics, autopsies, the gathering of evidence, the use of search warrants and interrogation.