In many ways, the Police Procedural is the opposite of the classic “whodunit” mystery. Rather than a private or amateur detective who succeeds by working in a typically unconventional manner outside the regular police force, the police procedural attempts to depict the workings of a real police investigation as accurately as possible.
The Procedural thrusts the detective into the middle of a working police force, full of rules and regulations. Instead of bypassing the police, as did its predecessors, the procedural takes the reader inside the department and shows how it operates. These are stories not just about policemen, but about the world of the policemen. (American Police Procedural).