Shane Black disliked the sequels, mainly due to how much of his script for the second film was re-written. He also said how the problem with the final version of the second movie was that they did too much comedy, and how he dislikes the other two sequels of the film because of the way they ruined Riggs' character (in his opinion, anyway).
Jeffrey Boam was unhappy that his script for Lethal Weapon 3 was largely thrown out and heavily re-written by Robert Mark Kamen. Similarly, his initial draft for Lethal Weapon 4 was unused, and his later contributions to the shooting script went uncredited due to the hectic production schedule. Boam later went on to say that both films were inferior to his original treatments.
Fake Nationality: In an odd reversal of Jewish actors portraying Italian-Americans, Italian-American actor Joe Pesci plays Leo Getz, a character of German-Jewish descent.
48 Hrs. from 1982 should be considered the origin of the 1980s buddy-cop film, but the Lethal Weapon series does codify most of the tropes.
Playing Against Type: Kind of; Leo Getz, like most of Joe Pesci's characters, is a hot-headed little guy with a Hair-Trigger Temper, but where most of Pesci's well-known characters tended to back this up by being genuinely dangerous and often psychotic thugs, Leo's pretty much harmless, a bit of a Butt-Monkey and for all his bluster a pretty nice guy.
Throw It In!: Leo's rants about people who fuck you with various goods and services, (The drive-thru, the hospital, etc.) are improvised. In fact, when he goes on his rant about being fucked by the hospital in three, you can see Renee Russo start to crack up in one shot before it's cut to another. The rant he and Butters go on about cellphones in 4 is entirely unscripted, with Donner apparently just telling them to, "Bitch about cell phones for a while."
Writing by the Seat of Your Pants: Director Richard Donner and producer Joel Silver's tendency to make serendipitous, on-set improvisations and changes has made this series is infamous for it.
Dawson Casting: Rianne was supposed to be around 17-19, played by then 25-year old Traci Wolfe.
Deleted Scene: Riggs originally had a different introduction. In it, Riggs is sitting alone in a bar getting drunk. He finishes off one bottle of Jack Daniels and orders another, but the bartender, both concerned for and wary of Riggs, cuts him off. Riggs stumbles into the back and is accosted by two hoodlums. He tries to warn them off, but they don't listen. He ends up crippling them and the bartender is not surprised. He tells Riggs as a friend to get out. Richard Donner felt it was too dark to open the film with. He felt that with the show of violence, viewers would judge Riggs' character before they got the chance to know him. Hence, he changed Riggs' introduction to the lighter, funnier morning scene in his trailer.
The Blu-Ray release contains deleted scenes not in the Director's Cut. Murthaugh's family scene was longer, with him interacting with Carrie and chastising Rianne for spending money on shoes; the jumper scene is longer; the fight in the pool is longer; Josuha surprises Rianne and her boyfriend before kidnapping her (which happens offscreen); and Riggs reassuring Carrie they'll rescue Rianne.
Enforced Method Acting: In the scene where Riggs is contemplating suicide, there is an actual bullet in the chamber which Mel Gibson was pointing at his head, thinking that it would allow for a greater sense of portraying the scene realistically and dramatically—and foolishly.
In Memoriam: The film was dedicated to legendary stuntman Dar Robinson, who was killed in a motorcycle accident shortly after principal photography was finished.
Inspiration for the Work: Shane Black was inspired by Dirty Harry to create an "urban western" where a violent character "reviled for what he did, what he is capable of, the things he believed in" is eventually recruited for being the one that could solve the problem.
Missing Trailer Scene: Theatrical and TV trailers for the film show few deleted and extended scenes that were never released in full on any DVD or Blu-Ray release of the movie; Murtaugh saying "New Partner?" after he gets thrown to the floor by Riggs when they first meet and when he is told that Riggs is his new partner, Riggs and Murtaugh driving in the car and Murtaugh telling Riggs "Don't kill anybody" and Riggs repeats the same line, couple shots of short deleted scene where Murtaugh is shooting his gun at target range alone, Riggs beating up two guys who try to rob and kill him while he is in the bar (original introduction scene for his character), and Riggs saying additional line "Nobody can touch me" after Murtaugh asks him is he really that good as he says he is.
No Stunt Double: Jackie Swanson did perform the high fall on her own. Trained by legendary stuntman Dar Robinson. Also, the stunt was done using an airbag covered with a life-size painting of the driveway and cars, which, like a foreground miniature, visually blends into the real scene. Thus, the editor is able to hold the shot until just as she makes contact with the airbag, for greater realism.
Danny Glover was primarily a character actor in supporting roles before the original film proved that he was a capable leading man.
Underage Casting: Danny Glover was only 40 years old when he was playing 50 year old Murtaugh. Even more amusing is that the actress who's playing his younger wife, Darlene Love, was actually five years older than Glover in real life.
Riggs is supposed to be in his late thirties to early forties, but Mel Gibson was only 30 at the time of filming.
According to a 2016 interview with Joel Silver, Ridley Scott was his first choice to direct the film. Due to Scott's still recent tensions with Warner Brothers, during the making of Blade Runner, the studio refused to offer him the job.
Leonard Nimoy was one of the choices considered for directing, but he didn't feel comfortable doing action movies, and he was working on Three Men and a Baby at the time.
Shane Black's original draft was much darker and more violent. The sniper scene in the Director's Cut one dead kid being carried on a gurney and the draft ended with a big chase scene including a police helicopter which gets blown up by Joshua who fires napalm missile at it causing it to crash into the Hollywood sign and start a huge fire, Murtaugh killing General McAllister while he is driving a a trailer truck full of heroin and guns which then crashes and explodes over Hollywood Hills causing for heroin to start snowing over the burning Hollywood sign, and Riggs killing Joshua by stabbing his finger through Joshua's eye right to the brain.
Riggs was a much different character in the first draft than he is in the movie, and lot more mentally unstable. For example, in the original version of the scene where he kills a sniper who is shooting at the kids, instead of using his gun Riggs uses a rocket launcher to blow up the sniper after he shot and killed several kids. In another part of the script he also uses ninja throwing stars to wound one of the villains and then tortures him for information. He and Murtaugh both had flashbacks of their time in Vietnam, with Murtaugh at one point remembering how he accidentally killed a young soldier with his bare hands during intense military training even before he went to war, and Riggs remembering how great killing machine he was and how much people he killed working as an assassin for CIA, which is why US and VC soldiers considered him a legend.
The Danza: In the second film, the carpenter is named McGee. This is the actual surname of the actor portraying him, Jack McGee.
Fake Nationality: None of the Amoral Afrikaners are played by actual South Africans. Joss Ackland (Rudd), Patsy Kensit (Rika), and Jim Piddock (Steyner) are English, Derrick O'Connor (Pieter) is Irish, and Mark Rolston (Hans) is American.
Throw It In!: Jack McGee ad-libbed his line about the condom commercial during rehearsals. The cast and crew liked it so much it was kept in the film.
The original script was different. Leo Getz being only a minor character and having only one scene and few lines of dialogue. Lot more violence throughout like South African villains, who were even more vicious in original script than in the final film, torturing Shapiro, a female police officer working with Riggs and Murtaugh (the one who is killed by a bomb in the pool in the film) to death in a very nasty scene. There was also a scene where Riggs is tortured by South Africans in a similar way like he was in the first film but much worse. The script also included an action sequence in which plane full of cocaine gets destroyed causing for cocaine to fall all over L.A like snow. The ending of the script included climactic battle which took place at hills engulfed with big brush fire, and after the destruction of the stilt house, Riggs chases Benedict (original name of the villain Pieter Vorstedt from the movie) who was different and lot more dangerous character in original script and Riggs' "arch-nemesis, his worst nightmare" as Black himself said, into the fire. After the final battle with Benedict, Riggs dies very slowly after he gets stabbed by him. The last scene in Black's script was Murtaugh watching the video tape that Riggs made earlier since he had a premonition that he was going to die and in which he says his goodbye to Murtaugh.
Joe Pantoliano was the first choice to play Leo, but he turned it down, due to a schedule conflict with The Last of the Finest. Danny DeVito was also considered
Originally Rika was not going to die, and in fact one of the earliest scenes shot was a different ending where she attended Thanksgiving with the Murtaughs. Director Donner changed his mind on this, as he wanted a bigger reason for Riggs to kill the diplomats.
Writing by the Seat of Your Pants: Shane Black and Warren Murphy's treatment was deemed too dark and depressing and was heavily rewritten by Jeffrey Boam, who had served as an uncredited script doctor on the first film. However, Donner and producer Joel Silver insisted on near-constant on-set revisions, necessitating an uncredited Robert Mark Kamen to rewrite much of the characters' dialogue mere minutes before filming. Almost all of the villains' dialogue exchanges were penned by Kamen during principal photography.
California Doubling: In the case of California Doubling, it's Inverted. The guy who says "Bravo" after the first building was blown up? None other than Bill Frederick, then the mayor of Orlando, Florida. The building used was Orlando's old City Hall building. Those familiar with the city will also recognize the SunTrust Center, the Orlando Utilities Commission building, and the new/current City Hall (which had a Coca-Cola sign planted on it). You can even make out a TV van from local ABC affiliate WFTV during the implosion.
The building imploded in The Stinger was in St. Petersburg, Florida.
Fake American: Ex-LAPD Corrupt Cop Jack Travis and Internal Affairs Chief Herman Walters are played by Briton Stuart Wilson and Canadian Alan Scarfe respectively.
Prop Recycling: In the scene where Riggs is in Lorna's apartment and he plays with her computer, the picture of the two boys seen on her mantle is the same picture used in Scarecrow and Mrs. King.
Throw It In!: When Lorna Cole says to Riggs "Close is a lingerie shop without a front window," Riggs doesn't know how to react to the comment. This was an ad-lib by Rene Russo. So not only does Riggs not get it, Mel Gibson doesn't either.
In earlier drafts, Lorna was completely different, had a different name and wasn't a woman, and was actually just as lethal and crazy as Riggs which made him his match. Riggs did however still had different love interest in those drafts. He was actually having an affair with Roger's oldest daughter Rianne, which explains a couple of parts in the finished film where Roger suspects that Riggs and Rianne are having an affair. Those parts are only bits left from original drafts where the two of them were a secret couple.
Leo Getz was originally not in the script and all of his scenes were written in afterwards. In the original script Leo had left L.A. for New York.
Writing by the Seat of Your Pants: Richard Donner's dissatisfaction with Jeffrey Boam's treatment led to the writer being fired and replaced altogether by Kamen, who made constant revisions between 1989 and 1991 before the producers rehired Boam to make new revisions to Kamen's material. Boam asked to work alone on the script, and made constant revisions between October 1991 and January 1992 while filming was already taking place. Boam and Kamen moved onto other projects, leading to Carrie Fisher to step in as on-set script doctor and writing most of the romantic exchanges between Riggs and Lorna Cole.
Playing Against Type: Jet Li was delighted to get the role of Wah Sing Ku because in China he is repeatedly type cast as a hero and he revelled getting a chance to play a villain for once. He would play villains in other American movies afterwards, but this was his first real bad guy role.
Star-Making Role: The film was responsible for introducing American audiences to Jet Li - doubly so as he played the main villain, which helped break his typecasting as strictly heroic characters.
Butters was originally going to be a gay character but once filming started, everyone involved realized how the decision to make him gay didn't work, so his character was re-written again to be a husband of Roger's daughter Rianne.
Originally, Mel Gibson insisted his character be killed off in the movie, as he felt this should be the last movie. After filming was completed, he retracted his statements, saying he had such fun making the movie, he'd be happy to do another one. The film teased fans with his original statements by hinting he was going to die by drowning after the concrete slab fell on him while Murtaugh was still unconscious.
Writing by the Seat of Your Pants: The film was fast-tracked into production without a script, leading to it being written on-the-fly during principal photography by no less than four credited writers (Channing Gibson, Jonathan Lemkin, Alfred Gough, Miles Millar) and at least three uncredited contributors (Tony Gilroy, Jonathan Hensleigh, Graham Yost). In the end, Gibson was given a screenplay credit, while Lemkin, Gough, and Millar were given a "Story by" credit.