The scene in the coffee shop was improvised. On the DVD commentary, Spike Lee states that when Denzel Washington ad-libbed the line, "I'll bet you can get a cab though," he nearly ruined the take by laughing so loud at Washington's line.
The scene, in which the boy shows the video game he is playing on his PSP to Dalton, was not in the original script. Director Spike Lee added it to "make a comment on gangster rap's infatuation with violence." The game is not real, but was created by an animation house. Lee asked them to come up with animation for "the most violent game ever".
According to Spike Lee, he and Willem Dafoe met in the men's room during the intermission of the play 'Julius Caesar', in which Denzel Washington appeared. As they were standing side by side in the men's room, Spike said: "We should work together" and Dafoe replied: "Yeah, Spike, we should" and that was it. Later on, Spike sent him the script.
Paul's (Lemon Andersen) line, calling one of the detectives that were interrogating him a "wassa-wassa", was improvised. So was Detective Frazier's (Denzel Washington's) response: "How do you say 'Rikers Island' in Spanish?"
The barber, in the scene at the exclusive men's club where Jodie Foster confronts Christopher Plummer named Vincent (his nameplate is affixed to the mirror, and Plummer addresses him by name too), is in real-life, the barber at the Down Town Association on Pine Street.
Spike Lee says that, at the time of making the movie, he was not aware that riddles had been a major part of the plot in another thriller set in New York City, Die Hard with a Vengeance (1995). He said if he had known that, he would have cut out the riddle scenes in his movie.
The line: "Detective First Grade Keith Frazier.....Yesss!!!" is a tribute to New York Knicks former long-time announcer Marv Albert. After a basket was made by 1970s New York Knicks star Walter Frazier, Albert would say: "Walt Frazier shoots....Yesss!!!"
The soundtrack for Inside Man features the song "Chaiyya Chaiyya", composed by A.R. Rahman, which originally appeared in the Bollywood Hindi film Dil Se.. (1998). The song is featured during the opening credits of the film. A remix of the song, titled "Chaiyya, Chaiyya Bollywood Joint" plays during the end credits, and features Panjabi MC's added rap lyrics about people of different backgrounds coming together in order to survive.
It is mentioned several times that Frazier is under investigation for a large sum of money that went missing on a previous case. Denzel Washington also played a similar character in The Taking of Pelham 123 (2009). The character was a protagonist attempting to thwart criminals while a pending investigation for a large sum of money was looming over him.
After Madeleine (Jodie Foster) first meets with Dalton (Clive Owen), she is debriefed by Detective Frazier (Denzel Washington). During the debrief, Frazier asks if Dalton is, "smarter than me? One of your types...Ivy-League type?" Jodie Foster graduated from Yale University; an Ivy League school. Much of the dialog in the film was improvised and it appears that Denzel Washington improvised this line because Foster's scripted response is interrupted and there is a slight awkward pause.
The shoot-out sequence between the police and the robbers was not in the original script. Spike Lee said he added it because he felt that "it was a good time to interject some action" in the movie. This scene was the last one, it was filmed on the last day so they could "shoot up" the bank movie set.
During the interrogation scenes, and when the hostages are being placed on police buses to be taken to headquarters for questioning, the audience learns the real names of Dalton's robber accomplices. 'Steve' is Kenneth Damerjian, 'Stevie' is Valerie Keepsake, and 'Steve-O' is Darius Peltz.
According to Frazier's promotion certificate revealed in the final scene, we know that the final scenes in the movie took place on August 12, 2005. We also know from the comments Russel's cohorts made when they were waiting to pick him up that he had been inside for a week. If the cohort's weren't exaggerating, this means the majority of the movie takes place on August 5, 2005 which was a Friday. This makes sense since the bank would be packed with people on a pay-day.
There are several instances of product placement in the film, such as an iPod seen playing propaganda messages, the Dell computer boxes covering the entrance to Dalton's 'cell', Madeline White's Apple Cinema Display and Hermès Birkin Bag, the Sony PSP owned by the little boy, the Chevrolet van used to transport the crew to the bank, and the Volkswagen SUV, which is used to pick up Russell. A North Face backpack was used to carry the diamonds out of the bank. Also, Poland Springs water, Pepsi, and Wrigley's Juicy Fruit are shown.