In any genre there are identifiable sub-classes that share conventions with the genres but also have their own distinctive subject matter, style, formulas, and iconography.
TV Crime Drama has its own sub-genres. There are many different ways of categorising these programmes below are some examples.
Individual Detective: eg Morse
Female Detective: Miss Marple
Paired Detective: Starsky and Hutch
Forensic: Silent Witness
Police Procedural: The Bill
American: CSI
Period: Life On Mars
Post-Modern: Dexter