It does seem to be true, as if some multiculti version of the Hays Code were in force, that in movies and TV shows, some good proportion of righteous law enforcement officers must be black, while only a negligible proportion of offenders can be.
We have so internalized this convention that I got a jolt the other day watching, on YouTube, some episodes from an old British TV series, Minder.
Minder was a crime-lowlife buddy-dramedy (got that?) on British TV from the 1979 fall season on. IMDb says it ran until 1994, but its greatest popularity was in the early 1980s, leading to much pop-sociological commentary about how it advertised Thatcher-era ethics, etc., etc.
“Minder” is London underworld slang for “bodyguard.” From the IMDb plot summary:
Arthur Daley, a small-time conman, hires former boxer Terry McCann to be his ‘minder,’ so Terry can protect him (Arthur) from other, small-time, crooks . . .
Alfie Cavallo, a friend of Arthur's, asks for the loan of Terry's services when he goes to collect the takings from one of the launderettes [=laundromats] he owns. However, Alfie and Terry walk in on an armed robbery by a trio who claim to be the Independent Rastafarian Army. Alfie is shot and the two men are taken hostage along with elderly customer Mrs. Mayhew . . .
The lead robber and his two juvenile sidekicks are all black. Everyone else, including all the police, are white.
The whole thing is much more good-natured than any equivalent could be under todays' regime of straitlaced puritanism, even assuming an equivalent could be made.
Here, at 16m34s on the YouTube showing, the lead robber has a gun at Terry’s head, and is telling him what to say to the police on the other side of a closed door.
Terry: “This is no ordinary robbery. This is a political act . . . This is a demonstration for equality and freedom . . .”
Policeman: “Exactly what political group do you represent?”
Terry: “We more or less represent a broad spectrum.”
Policeman: “Oh yes? Irish?”
Terry (after glancing back at the robber): “Er, not so’s you’d notice, no . . .”