Not only was this Jet Li's first American-produced movie, it was also the first time he'd ever played a villain.
Richard Donner asked Jet Li to slow down during action sequences, because he was moving faster than the camera shutter speed, and it wasn't registering on film.
Murtaugh's boat is named "Code 7", which is the L.A.P.D. radio code for a lunch break.
Jackie Chan was considered for the role of Wah Sing Ku, but turned it down, because he chooses never to play the villain in a movie.
The name of the police psychiatrist, who appeared also in the former three Lethal Weapon movies, is finally revealed in this movie - Dr. Stephanie Woods.
Chris Tucker, Will Smith, Eddie Murphy, and Larenz Tate were considered for the role of Lee Butters. Tucker would eventually go on to play a similar wisecracking detective along with Jackie Chan (who was also considered for this film) in their own buddy cop film, starting with Rush Hour (1998), also released the same year as this film.
Started filming in January, seven months before its release date. The shoot ended exactly 33 days before the release date. According to Editor Frank J. Urioste, to meet the deadlines, he had to use Avid, even though he had never edited a whole movie using digital technology before.
After Joe Pesci' and Chris Rock were hired at the last minute to play characters of Leo Getz and Lee Butters, characters who weren't in original script, some re-writes had to be done during filming to include both of them into the story. Pesci was hired at the last minute for one million dollars for three weeks of work, and Screenwriter Channing Gibson was three-fourths through his latest draft, by the time Chris Rock was hired. Butters was originally written to be a gay police detective, 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 the husband of Roger's daughter Rianne.
The only Lethal Weapon movie in which Riggs is not seen smoking. He was kicking the habit during the third one, and it is presumed that he kicked the habit by the time the fourth one began.
Roger Murtaugh's (Danny Glover) line of "I'm too old for this shit!" has made its way into every Lethal Weapon movie. Only this time, Riggs amends it to "We're not too old for this shit!" as a sign of defying their ages.
The car chase and fight between Riggs and the Chinese man in the house trailer was filmed on I-215 in Las Vegas, Nevada. Apparently, they couldn't get filming permission anywhere else, but the Las Vegas mayor was very accommodating. All drivers were either stunt drivers, or members of Bill Young's Driving Team.
When Riggs and Lorna were having the discussion about her hearing a rumor that Murtaugh was "on the take." Riggs jokingly said "I've tried to convince him to take money." In Lethal Weapon 2 (1989) when they were both trapped in a storage container filled with the drug dealers' money, Riggs did try to convince him to take some of the money and do something good with it.
Jeffrey Boam, who worked on uncredited re-writes for Lethal Weapon (1987) where he added some more humor into the script, after Richard Donner thought the original script was too dark, did a complete re-write of the script for Lethal Weapon 2 (1989), after the original draft by Shane Black and Warren Murphy was rejected for being too dark and bloody, and because Riggs died at the end, and wrote the script for Lethal Weapon 3 (1992), wrote a completely original script for a fourth Lethal Weapon movie, which everyone at Warner Brothers had liked, but was not used. Boam's unused script was built around Riggs and Murtaugh dealing with neo-Nazi survivalists, who were launching a terrorist attack in Los Angeles. This script was written sometime in January of 1995, and according to Boam, it dealt with real-life neo-Nazi activity in the U.S., that was only superficially dealt with in only one movie before, Dead Bang (1989). It was also going to be more serious sequel, much like the first film, and was going to be darker and edgier. Interviewed after the release of this movie, he remarked that he thought the counterfeiting of Chinese money was hardly a matter to create the suspense appropriate to a Lethal Weapon film, and also said how his script was much better from the final movie, which suffered some problems with constant re-writes, and actually didn't have a completed script during filming.
Despite Butters (Chris Rock) and Rianne (Traci Wolfe) being married, with a baby on the way, they never say a word to each other out loud. That's because their characters weren't originally written as a secret couple, but because of the many re-writes of the script, Butters was turned from a gay detective into Rianne's husband.
Warner Brothers decided during the scripting process, that the only story line they wanted to do involved Chinese immigrants in some way. Several writers worked out of this basic outline, with Channing Gibson earning the assignment. The story elements involving the Triads and corrupt officials were added, once the film was green-lit.
Only Lethal Weapon film not to feature any scenes in Murtaugh's bathroom. The first one had the birthday cake scene in the beginning. The second one had the toilet bomb scene. The third one had the retirement cake scene toward the end.
Jeffrey Boam's script for fourth Lethal Weapon film (one which had Riggs and Murtaugh fighting against neo-Nazi terrorists) wasn't the only version of the script for the film which was rejected. There were several others, including one which had Irish gangsters as main villains, and which ended with Riggs in a bare knuckle fight against the strongest and biggest one of them.
Four actors and four actresses have played the same characters in all four Lethal Weapon films. Aside from Mel Gibson and Danny Glover as Riggs and Murtaugh, respectively, Darlene Love plays Murtaugh's wife, Traci Wolfe, Damon Hines, and Ebonie Smith are Murtaugh's kids, Steve Kahan is Captain Murphy, and Mary Ellen Trainor plays Dr. Woods, the police psychiatrist. In a way, Riggs' dog, Sam is the ninth regular character. He appears in Lethal Weapon 1 and 2, and a deleted scene featuring him was reinstated for the Director's Cut of Lethal Weapon 3 (1992). Of those 9 characters, Captain Murphy was the only one never to appear at the Murtaugh residence at any point during the 4 films. Sam the Dog appeared at the Murtaugh residence at the end of the first film, and Dr. Stephanie Woods appeared at the Murtaugh residence during the toilet bomb scene in the second film.
One of the reasons why producer Joel Silver hired screenwriter Channing Gibson to write the script for Lethal Weapon 4 is because he liked the work Gibson did on re-writes of the 1993 spec script by other screenwriter Steven Maeda, titled Sandblast. Around 1995 and 1996 it was going to be made into an action thriller (described as both Die Hard and Cliffhanger in sandstorm) starring Wesley Snipes as army specialist and mine expert who has to work with team of US commandos and find several lost nuclear warheads in Iraq desert wasteland during huge sandstorm, before team of traitorous Green Berets finds them first, and Jean Claude Van Damme would play the main villain and leader of Green Berets, but that entire project got cancelled.
Riggs' trailer is in the same place that Jim Rockford's trailer was during the majority of The Rockford Files (1974)'s run.
This is the last of six times Richard Donner and Mel Gibson would work together. Their first collaboration was Lethal Weapon (1987).
The final film in which Michael Kamen composed the music for Joel Silver. The other films he'd worked on with Silver were, Lethal Weapon (1987), Die Hard (1988), Road House (1989), Lethal Weapon 2 (1989), Die Hard 2 (1990), Hudson Hawk (1991), The Last Boy Scout (1991) (a film which Kamen and Silver themselves hated), Lethal Weapon 3 (1992), Assassins (1995), Fair Game (1995) (in which his music was rejected in both cases), and finally this film. Kamen would pass away from Multiple Sclerosis in 2003.
The film's screenplay was in flux all the way from development through the entire production schedule. Channing Gibson, who took on primary scripting duties due to his longstanding work history with producer Joel Silver, was a successful television writer who was looking forward to the more relaxed pace of screenwriting, ended up going through more revisions than any television show he'd worked on. Amongst other things, the character of Lee Butters was not in the original script, and hastily enhanced when Chris Rock signed on, and Joe Pesci's Leo Getz wasn't slated to be part of the film until Richard Donner and Silver recruited Pesci to reprise his role.
On the Beretta 92fs, a button on the right side of the frame must be pushed in to un-block the lever on the left side, which is rotated down ninety degrees, in order to release the slide so the weapon can be 'stripped' and cleaned. It is possible to grab the gun, push the tab down, and pull the slide off to disarm the weapon. When Wah Sing Ku pulls the slide off of Riggs' Beretta 92fs, the button has already been pushed down and the lever partly rotated.
The previously unexplained source of the Murtaugh's wealth, in the film series version, is finally revealed.
Originally the final fight was supposed to be between just Riggs and Wah Sing Koo. However after a rehearsal where Jet Li not only blocked Gibson's punch, but delivered at least 20 blows to the actor too fast for the camera to see until the footage was slowed down, it was decided that there was no way the audience would buy Riggs defeating Wah Sing Koo alone.
Promotional television ads and the theatrical trailer featured Chris Rock wearing a police uniform doing a comedy act (he is referring to himself as Riggs being cast with a different actor - himself). His character never wore a police uniform in the movie. During the photo album credits, a picture of him wearing the uniform can also be seen.
In one scene, Riggs and Murtaugh congratulate one another on their promotions by rapidly alternating between handshakes and salutes. This is similar to scenes in Forever Young (1992) between Mel Gibson and George Wendt.
The only Lethal Weapon movie that doesn't have a Director's Cut on VHS, DVD, or Blu-ray. This is due to the theatrical release being the Director's Cut.
Warner Bros only took a decision to green light Lethal Weapon 4 late in 1997 realising they had no big tentpole releases scheduled for summer of 1998. In fact production on the movie began in January 1998 while the final third of the movie had not even been written.
In a scene in the police station the viewer can see posters advocating gun control. This drew some criticism in certain circles and even some unintentional humor due to the earlier films near glorification of weaponry and the sometimes over the top use of said weaponry by the police officers in the films.
In Lethal Weapon 3 (1992), Captain Murphy told Riggs to get a haircut. In this one he appears to have gotten a haircut.
Paul Tuerpe appears in all four Lethal Weapon movies, but always in slightly different roles. He played 'Mercenary' in the first, 'Hitman' in the second, 'Henchman #3' in the third, and 'Helicoptor Co-pilot' in the fourth.
Cellular telephone technology evolved considerably over the eleven-year course of the Lethal Weapon series (1987-1998), as is showcased during the scene when Butters and Leo Getz discuss cell phones and cell phone company scams. Butters mentions cell phones as being made smaller and smaller so that people will be more likely to lose them. The cell phone Butters had was far smaller and could easily be stored in pockets, when compared to the original cellular phone showcased in Lethal Weapon (1987), which were far too big for people to fit in their pockets, or on a belt holster.
The only Lethal Weapon movie that was only number one at the box-office its opening weekend. The other three were number one three weeks in a row.
One of the Pontiac Grand Ams used in the film was on display at Warner Brothers Movie World, Gold Coast, Australia, for several years, before being auctioned off, along with other items from the park, in late 2012.
WILHELM SCREAM: At the beginning of the film, when Riggs shoots the man with the flamethrower, sending him flying into the gas station, a muffled Wilhelm scream can be heard.
The name of the character played by Jet Li is never mentioned until the end of the movie. It is revealed when Riggs asks Detective Ng. The character's name is Wah Sing Ku.
The second locomotive that strikes the bad guys' car in the second railroad crossing scene is the same former Alaskan Railroad GP7-type locomotive No.1804, which was at the front of the Grand Continental train in Under Siege 2: Dark Territory (1995). It has the same livery, with the Grand Continental names removed.
Leo and the main cast refer to themselves as family. This harks back to Lethal Weapon 3 (1992). When Lorna first encounters Leo, she asks who he is and Riggs says, "He's family."
According to Behind the scenes footage, Rene Russo was very scared of being hit for real during the filming of the scene where Wah Sing Ku knocks Lorna out with a single kick to the head. So much so in fact that she refused to open the door for a few moments while the cameras rolled.
Al Leong, who played the mercenary known as Endo in Lethal Weapon (1987), appeared in an uncredited role as a Wah Sing Ku Triad member.
Danny Wynands has a role in all of the Lethal Weapon sequels. Wynands and Joe Pesci were the only actors to appear in approximately 3 films in the franchise. They were both absent from "Lethal Weapon" (1987), but appeared in all 3 sequels.
This is the first Lethal Weapon film that Mel Gibson wears a leather jacket (in Lethal Weapon 2 (1989) he sports a letterman jacket), and doesn't wear blue jeans.
Kim Chan (Uncle Benny) says, "Bloody marvelous!" a catchphrase often used by his character "The Ancient" in Kung Fu: The Legend Continues (1993).
After being promoted, Riggs addresses Murtaugh with the words "O Captain, my Captain", which is the title of a poem by Walt Whitman (and, of course, a reference to the Dead Poets Society (1989) where the phrase plays a central role.)
Many gun owners and NRA members were displeased with the overt anti-gun messaging in this movie, and actively boycotted it. Clear examples of this are the protagonist calling the active shooter an "NRA spokesman" within the first few minutes of the film, as well as the two prominent Anti-NRA and pro "assault weapons" ban posters in the police department's lobby. Richard Donner, the director, made clear in a Variety interview that the messaging was intentional, claiming "I do it in almost every picture of mine". Many accounts also claim that Danny Glover was complicit in requesting the message be pushed.
The second Lethal Weapon movie to feature the casting credits at the end of the movie, as opposed to the beginning. The first of the series to do this was Lethal Weapon 2 (1989). Both Lethal Weapon (1987) and Lethal Weapon 3 (1992) had their casting credits at the beginning of the movie.
Only Lethal Weapon film in which Riggs does not drive a GMC Sierra with dual rear wheels. In this film, Riggs drives a GMC Sierra with single rear wheels. It is also the only film in which Riggs drives a GMC truck with four-wheel drive (the trucks in the first three films were only two-wheel drive).
Each Lethal Weapon film features a bad guy with glasses. Here, in the fourth one, it is the older triad, whose glasses are broken at the prison in China, and replaced after arrival in America.
Riggs is using a Beretta 92fs with a Lasermax laser sight, a special kind of laser sight that replaces the standard spring guide.
This is the only Lethal Weapon film where the official release is the Director's Cut.
Gibson's character Riggs mockingly calls Jet Li's Wah Sing Koo "Bruce" in reference to Bruce Lee. Ironically while he had tried to distance himself from the legendary actor/martial artist, Jet had recently made a remake of Lee's Fist of Fury (1972) with Fist of Legend (1994). His outfit as Wah Sing Koo even resembles the one he wore in the former film.
The end hospital scene has two actors from Fletch (1985). Richard Libertini is Fletch's boss, and here he is a Rabbi. Bill Henderson is the speaker at Fred Dorfman's party, and here is the Angry Patient with Urine Sample.
In reference to Butters supposed to being gay you can dialog by Roger asking Martin if he thinks Butters is gay. There are several lines suggesting that in the film.
In the beginning of the movie, the man with the flame throwing begins playing the song "Fire In The Hole." by Van Halen. The song, which can be found on the album Van Halen III, featured ex-Extreme front man Gary Cherone on lead vocals. Since Cherone was fired not long after the album came out, this is the only time a Van Halen song appears in a movie without either David Lee Roth or Sammy Hagar on lead vocals.
After Simon Rhee and Jeff Imada work together in Lethal Weapon 4, they work together again in Blade with Wesley Snipes.
In one scene, Riggs references the Jim Carrey films "Ace Ventura: Pet Detective" (1994) and "Ace Ventura: When Nature Calls" (1995), the former directed by Tom Shadyac. The second Carrey/Shadyac collaboration, "Liar, Liar" (1997) featured Mitchell Ryan, who played General Peter McAllister in "Lethal Weapon" (1987).