Much like its sister show Homicide: Life on the Street, contains numerous references to David Simon's book "Homicide: A Year On The Killing Streets". For instance, the opening of the very first show is lifted directly from the book.
The character of Sgt. Jay Landsman played by Delaney Williams was based on Jay Landsman, a real-life Sergeant with the Baltimore County Police. He was featured in David Simon's book "Homicide: A Year On The Killing Streets". Landsman himself joined the cast in the third season playing Lt. Mello.
Jay Landsman auditioned for the character based on himself before being cast as Dennis Mello.
Many of the minor characters are played by real-life police officers, politicians and former criminals. In fact, many of the former criminals who act on the show were previously arrested by the real-life cops who act on the show.
The character of Avon Barksdale is loosely based on Melvin Williams. Williams was a notorious drug kingpin in Baltimore who was brought to justice by Ed Burns.
Tray Chaney originally auditioned to play the character of Wee-Bey Brice but the producers felt he was too short. They were so impressed with his audition that they created the character of Poot for him to play.
David J. Smolar, who appears in the final episode of season 3 as a reporter talking to Councilman Gray, previously appeared as the piano player in a restaurant scene between D'Angelo and his girlfriend in episode 5 of season 1. Smolar performed the piano music heard in that episode, a posthumous Chopin Etude and later movement 2 of Beethoven's Pathetique Sonata.
In most episodes, subpoenas are issued by "Larry W. Shipley, Clerk of the Circuit Court." Mr. Shipley is, in reality, the former Clerk for Baltimore's neighboring county, Carroll County.
SPOILER: Producer Robert F. Colesberry also plays Detective Ray Cole. After Colesberry died tragically following routine heart surgery, the Ray Cole character also died from a heart related illness in the show. The entire cast participated in an elaborate detectives wake in honor of Cole and Colesberry's memory.
The character of "Bubbles", played by Andre Royo, was largely based on a real Baltimore drug addict and police informant who went by that name. The real Bubbles, who would slur his speech much more than the fictional character, first started working with the cops near the early 1960's after being arrested for a burglary. He spent the next few decades as an informant, leading to the arrest of several hundred felons and getting paid at least $50 for each one caught. His photographic memory and ability to blend into the scene made him one of the best in the city. Eventually he would start using the hat method portrayed on the series, where he acted as if he was selling hats and would place one of a certain color on the head of those the police should arrest.
In season one, two detectives, Augustus Polk and Patrick Mahon - were assigned to the Barksdale detail. The names "Polk" and "Mahon" are a play on "pogue mahone," the anglicized version of an Irish expression meaning "kiss my ass."
The picture on Frank Sobotka's dartboard is of Bob Irsay, the owner of the Indianapolis Colts who moved the team from Baltimore in the middle of the night in late 1983.
Reg E. Cathey auditioned for the roles of Cedric Daniels and Lester Freamon. He was later cast in the show's fourth season as Norman Wilson.
Lance Reddick auditioned for the roles of Bunk Moreland and Bubbles before being cast as Cedric Daniels.
Anwan Glover auditioned for the roles of Marlo Stanfield, Fruit and Drac before being cast as Slim Charles.
Gbenga Akinnagbe auditioned for the role of Marlo Stanfield before being cast as Chris Partlow.
Jamie Hector auditioned for the role of Cutty Wise before being cast as Marlo Stanfield.
Jermaine Crawford auditioned for the role of Michael Lee before being cast as Dukie Weems.
Tristan Wilds auditioned for the role of Randy Wagstaff before being cast as Michael Lee.
Seth Gilliam auditioned for the role of Stringer Bell before being cast as Ellis Carver.
Isiah Whitlock Jr. auditioned for the role of Lester Freamon before being cast as Clay Davis.
When Dominic West first auditioned on videotape from his London home, he tried to have his girlfriend read the lines for the other characters in the scene. But her English accent kept throwing him off and he kept laughing. So West performed the scene himself by leaving pauses where the other character's lines were supposed to be. West admits to imitating Robert De Niro for his audition. At first, the producers found the audition tape "weird" and "comic" but they reconsidered when they concentrated on West's performance. When West was offered the role, he became reluctant because the contract was for five seasons. But his agent convinced him that the show would not last more than one. It ended up lasting five seasons.
The character of 'Bunk' Moreland is based on real-life Baltimore detective Oscar 'Rick'/'The Bunk' Requer. The real 'Bunk' also constantly chomped on a cigar.
Donnell Rawlings was considered for the role of Omar before being cast as recurring character Damien Price.
A spin-off was planned during pre-production on the fourth season. It was to be titled "The Hall" and focus solely on the politics storyline but HBO ultimately rejected the idea.
SPOILER: Although Cheese Wagstaff and Randy Wagstaff have the same last names, it is never stated that they are related. David Simon has since confirmed in interviews that Cheese is Randy's father. Simon planned to reveal this in a fifth season episode but later decided against it.
Michael Kostroff originally auditioned for the part of Frank Barlow before being cast as Maurice Levy.
Ranked #8 on Empire magazine's 50 Greatest TV Shows Of All Time (2008).
SPOILER: In an unusual move for a police series the officers almost never fire their guns. Only one police officer, Prez, ever fires his gun on the show and in all three cases it is a mistake. The first time he accidentally shoots the squad room wall. The second time he drunkenly fires a shot into the air and then (compounding his gun mistakes) uses it to pistol whip a teenager, blinding him in one eye. The third time he mistakenly shoots an undercover cop.