In 1988, a Baltimore Sun reporter named David Simon joined the Baltimore Police Homicide Unit as a civilian assistant, in order to chronicle a year in the life of a big city homicide squad. His extensive notes, interviews, and observations were eventually published as the book, "Homicide: A Year On The Killing Streets." This book served as the inspiration for the TV series Homicide: Life on the Street (1993). Much of the first and second seasons are taken from actual events recounted in the book.
A real live criminal, on the run from the Baltimore Police Department, entered the set of Homicide: Life on the Street (1993) and surrendered to the actors in uniform. This incident was later spoofed in an episode where the actors in the show chased a suspect onto the set of "Homicide" and encountered the director, Barry Levinson, and several of their favorite actors from the show.
Detective Munch is mentioned in the BBC's crime drama Luther (episode 5). Luther instructs a subordinate to telephone Special Victims Unit in New York, specifically Detective Munch to garner information about the villain in the episode.
The board showing unsolved and solved cases for each detective was a real device used by the Baltimore Police Department. It was stopped when it was shown to bring down morale, but it returned later at the request of the detectives.
All of Detective John Munch's partners either retire or resign from the Baltimore Homicide Unit shortly after having been partnered with him... Bolander after season 3, Russert after season 4, Kellerman after season 6, and Bayliss after season 7.
Jon Polito originally read for the part of Detective Lewis but requested to be cast in the part of Crosetti. The character was not named Crosetti in the original script but the name was changed to reflect Polito's Italian heritage.
Five of Detective Steve Crosetti's cases are alluded to throughout the first three seasons, but none of the investigations appear in any given episode. Thus, the viewers never get to witness Crosetti be the 'Primary'.
The trivia item below may give away important plot points.
According to the audio commentary on the DVD, the writers added the plot twist about Pembleton's stroke to appease Andre Braugher, who felt that he'd explored his character to its limits, and wanted to leave the show. The character did recover much more rapidly and completely from the stroke than would have been possible in real life.