Originally Posted by
Tziva
The Wire is my absolute favourite TV series of all time, so that's always my vote.
It's not technically a prequel, but it's in the same vein.
David Simon, the guy primarily behind The Wire, has two books that made it into TV: Homicide, about Baltimore's homicide detectives and The Corner, about street-level drug trade in Baltimore. Homicide ended up 7 season TV series in the 90s (it's dated but good - and the origin of Richard Belzer's longrunning cross-series character John Munch). The Corner was an HBO docudrama miniseries (just six episodes) that came shortly after.
Both series share a lot of actors with The Wire. I can think of at least ten off the top of my head.