Mark Wahlberg based his performance on the police officers who'd arrested him about two dozen times in his youth, and the reactions of his parents who had to come bail him out with their grocery money.
Martin Scorsese really wanted Al Pacino for the role of Costello, because he had never worked with Pacino before, but he turned it down. Jack Nicholson was Scorsese's second choice. Pacino would later go onto appear in Scorsese's The Irishman (2019).
A possible reason why Leonardo DiCaprio did not receive an Oscar nomination for his performance in this movie was because Warner Brothers initially did not want to favor DiCaprio over his co-stars, and place him in the leading actor category. The studio favored DiCaprio's leading performance in Blood Diamond (2006), which eventually got him a nomination. DiCaprio refused to campaign against his male co-stars in the supporting actor category, so Warner bought no supporting actor ads for DiCaprio, and he did not receive a nomination.
When the film won the Oscar for Best Picture, Martin Scorsese said that he was surprised the film had won. Scorsese said that because the film is such a tough, nasty, and violent film, he never thought about the idea of awards while he was filming it.
Originally, Jack Nicholson turned down his role in the movie, but after a meeting with Martin Scorsese, William Monahan, and Leonardo DiCaprio, he was finally convinced to play the role of Frank Costello. The main reason he joined the production was because he had previously done a few comedies, and wanted to play a villain again, and he considered the character of Costello to be the ultimate incarnation of evil.
Martin Scorsese wanted to shoot the film in Boston, where the story is set. The bulk of the film was shot in New York, partly due to concerns about setting up production and politics, partly because of New York's 15% filmmaking tax credit. They shot in Boston for 3 weeks in June and 3 more in August. After the success of this film, Massachusetts created a 25% tax credit for filmmaking.
When Sullivan asks Trooper Barrigan, "Do you have any suits at home, or do you like going to work looking like you're going to invade Poland?", he's referring to the fact that the Nazis modelled their own uniform after Massachusetts State Police uniforms.
As research for his character's occupation, Matt Damon worked with a Massachusetts State Police unit out of Boston. He accompanied them on routine patrols, participated in a drug raid, and was taught proper police procedures, like how to pat down a suspect.
After completing The Aviator (2004), Martin Scorsese kept Alec Baldwin in mind for future collaboration and ultimately decided to cast him in the role of Ellerby, which was offered to Mel Gibson first, but Gibson was unable to accept the part, because he was starting production on Apocalypto (2006) at the time.
At the beginning, when the main characters are in a police academy ballistics lecture, the large flip chart illustrations seen in the background are Warren Commission exhibits of President John F. Kennedy's head wounds, prepared by medical illustrator H.A. Rydberg under the direction of Dr. James Humes, the chief examiner of Kennedy's autopsy. Texas Governor John Connally was also riding in the car that day, and was also shot. John Connolly is also the name of the FBI agent who recruited Whitey Bulger as an informant, and ultimately protected him from investigation or prosecution for many years.
Colin Sullivan's apartment does not exist. The view of the Massachusetts State House was an effects shot from the roof of Suffolk University, which is the law school where Sullivan says he is taking night classes. Cinematographer Michael Ballhaus evaluated the shot during pre-production.
When Colin has dinner with Madolyn, he states "what Freud said about the Irish is we're the only people impervious to psychoanalysis." According to the FAQ section of the Freud Museum in London, Sigmund Freud , "There is no evidence Freud said the quote. The only documentation seems to be Anthony Burgess, in his introduction to a book of Irish short stories: 'One of Freud's followers split up human psychology into two categories, Irish and non-Irish.'"
(At around one hour and seventeen minutes) It was Jack Nicholson's idea to film the scene when Frank Costello attends the opera. It was also Nicholson's idea to have one black woman and one white woman in the scene with him.
Screenwriter William Monahan envisioned a sequel to the film, citing that it would've focused on overlooked aspects of the first film, such as political corruption. Monahan had watched the sequels to the original film on which this movie was based, but felt that a potential sequel would've gone in a different direction set by this film. Mark Wahlberg also indicated that Dignam would've been the main character in this film. To date, plans for the sequel haven't materialized.
One of the reasons Martin Scorsese agreed to direct this movie, was because it reminded him of one his favorite movies White Heat (1949), a film noir starring James Cagney, also partly about an undercover police officer embedded with a charismatic gangster.
Thomas B. Duffy is a retired Massachusetts State Police Major, who worked out of Boston for nearly thirty years, and specialized in organized crime. He was particularly involved in the case against notorious South Boston mob boss James "Whitey" Bulger, on whom Frank Costello is partly based. Duffy appears as the Governor, who delivers a speech to the graduating police cadets. There was an unconfirmed sighting of Bulger, one of the F.B.I.'s Ten Most Wanted, at a theater showing the film by a Deputy Sheriff in San Diego, California. Bulger was captured in Santa Monica, California on June 22, 2011. He'd been living in an apartment complex just a few blocks away from the production offices of GK Films (U.S.), who produced Edge of Darkness (2010), in which Duffy also appeared.
There are two phone numbers used in the film. The first is Billy's phone number, which is 617-869-1469 (It appears when Colin Sullivan answers the phone). This is a real Boston number used by Sprint Spectrum. If someone calls it, you will get a generic voicemail box, which is full. The other number is 311-555-2368, which was a phone number used in telephone company publications.
The first Best Picture Oscar winner of the twenty-first century that wasn't released on VHS in the United States, and the first to be released on the short-lived HDDVD format. Warner Brothers Home Entertainment had already phased out VHS by 2006, therefore, the film was initially released on DVD, Blu-ray, and HDDVD the following year.
(At around thirteen minutes) When Queenan and Dignam are interviewing Costigan, Costigan says "Families are always rising and falling in America." Queenan wants to know who said that, and it turns out to be Nathaniel Hawthorne. Dignam quips, "What's the matter smart ass, don't know any f****n' Shakespeare?" Later (at around one hour and one minute), as Queenan hands the clipboard to Sullivan, it is Queenan who quotes William Shakespeare with "the readiness is all", from Hamlet's "Fall of a sparrow speech," Act V, scene II.
(At around one hour and fifty-five minutes) The newscaster seen reporting the news story detailing the dumped body by Costello's gang, was a real Boston area newscaster at the time of filming. He reported for Boston's Warner Brothers affiliate station WB56.
Denis Leary was offered the role of Dignam in this film, but turned it down due to scheduling conflicts with his television show, Rescue Me (2004). He was disappointed, but he did hold Mark Wahlberg's performance in high regard.
(At around nineteen minutes) Tom Kemp and Zachary Pauliks appeared in a flashback scene, in which Frank talks to Billy's father, as young Billy looks on. Although the scene was deleted, the actors appear in the picture that Billy gives to his aunt, and the actors are still listed in the closing credits.
Frank Costello (Jack Nicholson) was supposed to wear a Red Sox cap in the movie, but refused to. The hatred of Boston sports teams date back to the days of Nicholson's love affair with the Lakers and the heated rivalry with the Celtics. The Red Sox cap was the signature uniform of James "Whitey" Bulger, but Nicholson couldn't overcome his disfavor.
(At around one hour and seventeen minutes) Frank Costello attended the Gaetano Donizetti opera Lucia di Lammermoor. This is a musical homage to Scarface (1932), as Paul Muni's character would often whistle the sextet from this opera, whenever he killed someone.
Vera Farmiga was one of the only actresses who didn't watch Infernal Affairs (2002), the movie on which this is based. Madolyn is inspired by multiple characters, so Farmiga thought it would be confusing for her.
(At around forty-nine minutes) When Colin (Matt Damon) tells Fitzgibbons (David O'Hara) to call his mother from Trooper Brown's phone, the ringtone on the receiving phone is "Scotland the Brave", one of the tunes played on the bagpipes at the cadets' graduation ceremony.
(At around one hour and two minutes) During the exchange with the Chinese gangsters, Sullivan sends a text message to Costello saying that all cell phone calls are being monitored. The number dialed by Sullivan is a real Boston area code (617).
The classroom scene, police academy graduation scene, and shooting range scene (all at the beginning of the film) were shot near the end of production. Historic Ft. Schuyler on the campus of State University of New York's Maritime College was the backdrop.
The "MASS Processor Company's" microprocessor, shown in the movie, is really an ST Microelectronics' ST9F150JDV1QC micro-controller, released in 2003 and intended for applications such as MP3 players, GPS devices, and car radios. It went for around seven dollars at the time it was released (in the movie it is stated they go for one hundred thousand dollars each). The microprocessor has an internal clock frequency of twenty-four Megahertz and one hundred pins, and can hold up to four Megabytes of memory. A typical Intel Core 2 Duo microprocessor, released in 2006 (the same year as The Departed) for use in desktop computers, runs at 1,400 Megahertz or higher frequencies, has 775 pins, and can address up to four thousand Megabytes.
Captain Queenan mentions to Billy Costigan that his son attends Notre Dame. Martin Sheen's character from The West Wing (1999), President Josiah Bartlet, went to the same university, and was also a fan of the Boston Celtics.
During the scene where Mr. French (Ray Winstone) is throwing firecrackers, the song Baby Blue by Badfinger can be heard in the background. This song was also used in the final scene of the television series Breaking Bad (2008).
The trivia items below may give away important plot points.
(At around one hour and seventeen minutes) The scene where Frank Costello throws cocaine on hookers was one of many bizarre ideas contributed by Jack Nicholson, who also suggested wearing a strap-on for the scene with Matt Damon in the porn theater.
Many scenes with Jack Nicholson were improvised. Nicholson was given the opportunity to do whatever he wanted to add to the character's unpredictability. The scene where Billy and Frank are talking was loosely scripted, and many surprises happened in it, including Frank pulling out the gun.
Throughout the film, Martin Scorsese used Xs mostly shown in the background to mark characters for death. Examples include shots of Costigan walking through the airport while talking to Sergeant Dignam, Queenan falling to his death (on the building's glass windows as Queenan falls to the ground), and Sullivan in his office discussing the flow of information with Costello (the X is created by the light shining through the window). This is an homage to Scarface (1932).
At the beginning of the film, Frank Costello instructs the store clerk to fill a brown paper bag with various groceries for the kid Colin Sullivan, notably a couple of loaves of bread and a couple of quarts of milk. In the last scene of the film, we see adult Colin Sullivan walking into his apartment with a paper bag full of groceries, two of the items you can see in the bag during this scene are a couple of loaves of bread and a couple of quarts of milk.
The "Frank Costello" caricature is loosely based on James "Whitey" Bulger, who ran a Boston-based Irish gang while working as an FBI informant, protecting him from prosecution while he killed dozens of people. His FBI handler was convicted of multiple felonies.
At the end of the movie when Billy brings the tape to Madolyn, we can deduce that the child is not from Colin Sullivan, but from Costigan. She wants to tell him something, but he leaves right before she does. Sullivan also has, during a scene in the film, some "issues with what happened last night". Madolyn then sleeps with Billy.
Martin Scorsese expresses the highly unpleasant experience in making the film. He states "Moral Ground Zero, I call it, all the characters killed at the end, basically everyone, and there was no place to go, after that. You know, I hardly did any press for that film. I was tired of it. I felt it was maddening. I mean, I like the picture," he continues, "but the process of making it, particularly in the post-production, was highly unpleasant. I don't care how much I'm being paid, it'll kill me. I'll die. Very simply."
(At around five minutes) Right after the time skip in the beginning of the movie, during the first lesson at the police academy, the teacher is elaborating on the details of a gunshot wound to the head, which is the leading cause of the vast majority of deaths throughout the course of the rest of the movie.
(At around two hours and ten minutes) The CD that Costigan mails to Colin is mailed in the cover for The Rolling Stones' album "Exile on Main St." Earlier in the film (at around thirty-six minutes), when Costello beats Costigan's hand with his own shoe, a song from the album, "Let It Loose", plays over the scene.
When Billy Costigan interrogates the drug-addicted bank robber (Joseph Riccobene), who reveals to him that Frank Costello is an FBI informant, the television set in the bank robber's living room is playing the final scene from The Informer (1935). The movie has a similar plot, about an Irish nationalist, Gypo Nolan (played by Victor McLaglen in an Oscar winning role), who turns informant, and feels guilty after betraying a friend to the Irish "Black and Tan" police force.
(At around two hours and twenty minutes) In the final scene, as Sullivan walks to his apartment, the floor has large patterned Xs on the carpet. He walks over two of them as he approaches the door. It's as if to say strike one, strike two, and strike three being the coup de grace from Dignam.