Blue Streak (1999)

A former convict poses as a cop to retrieve a diamond he stole years ago. - MonkeykingMA

Miles Logan is a jewel thief who just hit the big time by stealing a huge diamond. However, after two years in jail, he comes to find out that he hid the diamond in a police building that was being built at the time of the robbery. In an attempt to regain his diamond, he poses as an L.A.P.D. detective... - Christopher Tilton

Miles Logan is a jewel thief. Things go awry while he's stealing a huge diamond in downtown L.A.: a thief, Deacon, tries a double-cross, the police arrive, and Miles is arrested, but not before he hides the jewel in an air duct of a building under construction. Two years later, he's out of prison and he heads for the site: it's L.A.'s new police headquarters! Posing as a reassigned cop, Miles gets into the building, but before he can recover the swag, he's partnered with a naive detective and sent out to investigate burglaries. With Deacon on his trail, he must recover the diamond, keep the cops fooled, and do a few good deeds as a detective who can think like a criminal.