Trivia: Kevin Spacey made sure that it was in his contract that his name would not appear in any press releases or reviews, that his photo would never appear in any of the above, he was not to be mentioned in interviews nor was his name to be anywhere in the opening credits. He cites his reason as being that The Usual Suspects and Outbreak were both opening earlier that same year and figured that people would start to recognize his name. And he also figured that if people saw his name in connection with the movie and he didn't appear for the first 2/3 of the movie they would know that he was playing the killer, thus ruining the element of shock and surprise that the moment in the movie has built up to. To compensate, Spacey is listed first in the ending credits.
Trivia: In 1998 Boris Starling wrote a book called "Messiah" which is a murder mystery similar to "Se7en" in that the protagonists are chasing someone who murders brutally and with Christian motif. The killer in that book is called Silver Tongue and believes himself to be Messiah. In this film Mills tells Doe that he's not Messiah, and Sommerset calls Mills Silver Tongue. It's kind of a neat thing to notice if you've read the book.
Trivia: I noticed this in a moment of intense boredom: On the deluxe special DVD edition of Se7en, Gwyneth Paltrow is credited on the back as 'Gweneth Paltrow'. Just a small, insignificant mistake, but as it's not part of the movie I thought it was a slightly interesting piece of trivia.
Trivia: The building in which Se7en's library scene was shot also featured as the bank in The Mask and several other movies. Director David Fincher jokingly remarked that it has been used in so many of New Line Cinema's films that the company could have saved money by buying the building outright rather than renting it for each production.
Trivia: Spoilers. The studio reportedly wanted to cut the ending because they felt it was far too dark and tried to commission several alternate versions in which Tracey's head was not in the box. This included producers trying to add in a twist where John Doe tells Mills that her head is in the box, when in reality it actually contains a dog's head, and an alternate version in which Tracey is merely kidnapped and being held hostage. Brad Pitt, David Fincher and Morgan Freeman all threatened to walk from the project if the originally planned ending wasn't included.
Trivia: An alternate version of the script was written that had a radically different ending that was considered. It would end with Mills being captured by "John Doe" and kept in an abandoned church, where he would be ritualistically tortured (including having a cross carved into his chest) and then strung up and shot through the heart, with Agent Somerset becoming "wrath" by setting fire to the church and killing Doe to get revenge. While a more cinematic and action-packed finale, this ending was dropped in favor of the ending that was eventually used.
Trivia: New Line Cinema tried for some time to make a sequel to "Seven/Se7en" in the early 2000's. A script about a psychic detective working with police to capture a murderer was purchased, and was quickly re-written to focus on the character Somerset from this film, who had somehow gained psychic abilities. The sequel would have had the title "Ei8ht." David Fincher was given a copy of the script and turned it down instantly, and later remarked that he would rather "put cigarettes out on [his] eyes" than make the film. The film was eventually made under its original title "Solace" and released in 2015, with Anthony Hopkins starring.