He was a Detroit detective that defied his Captains orders not to get involved in an investigation over his partners murder. He was then told to stay out of the investigation by the LAPD as well cause of his captains orders and went a head and did his own investigating and tipped off the detectives that were working the case...
Honestly he doesn't even need to be a cop in this one... he can just be a private investigator.. although, its called Beverly Hills Cop....