Spike Lee was facing a lot of negative feedback from the family members of the victims who didn't want a film being made which might glorify the killer in some manner. As a result, the script had to be changed which focused more on the community than the killer himself. "Son of Sam" was rumored to be the original working title.
The "I am the monster" letters read in the film are word-for-word recreations of those that the real Son of Sam wrote to Jimmy Breslin.
In the script, Richie was the lead character and Vinny was a secondary character. But Spike Lee enjoyed John Leguizamo's improvising so much that he ended up giving him more screen time. The scene where Vinny pours coffee on Gloria was one of many improvisations by Leguizamo.
Two minutes of film were cut, mostly from the club orgy scene, to get an R rating instead of an NC-17.
Reggie Jackson: There is an insert of Jackson during the scene when the mobsters are throwing out the theory that he is the killer due to his New York Yankees jersey number. While it looks like older footage, it was actually Jackson from 1999. In the Blu-ray commentary track, John Leguizamo asked Spike Lee if that was because it might be cheaper than to buy the real footage, and Spike replied, "No, I just really wanted to meet Reggie."
L.E.S. Stitches: The punk rock band playing at CBGB when Joey T (Michael Rispoli) and Brian (Ken Garito) go there to look for Richie (Adrien Brody). L.E.S. Stitches is an actual band that was founded in 1994 on the Lower East Side of Manhattan in New York City. The "L.E.S." in their name is an abbreviation for "Lower East Side".
Joie Lee: As a resident of the Bed Stuy section of Brooklyn, New York who local TV reporter John Jeffries, played by director and Lee's older brother Spike Lee, interviews after the Son of Sam commits his first murder in Brooklyn. Summer of Sam (1999) is the 8th Spike Lee Joint in which she has acted.