police procedural

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A story or drama about the investigation of a crime by the police.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun a sub-genre of crime fiction which portrays the activities of a police force as they investigate crimes. Unlike other types of crime fiction, the perpetrator may be known at the outset of the story.