Below is a list of  TV detective and police shows made available to watch online via Hulu, CBS, and In2TV. Most of these are not public domain but available through ad-supported watching

Adam-12

Adventures of Sherlock Holmes

Dragnet

Hart to Hart

Hawaii 5-0

Highway Patrol

Kojak

Moonlighting

New Dragnet

Perry Mason

The Rockford Files

Spencer for Hire

Starsky and Hutch

S.W.A.T.