Continuity mistake: In the scene where "the General" and his driver were fleeing down the alley, the driver is shot. The general takes control of the wheel and carries on driving, but the car is in park... (01:34:25)
Continuity mistake: The pattern of scars on Riggs' face changes when he comes to deliver his bullet to Murtaugh: The two cuts on his left cheek become three, and the lesions on his chin disappear. (01:39:40)
Continuity mistake: A quick shot from the interior of the General's car looking at the approaching bus, a metal guard is seen on the front of the bus, painted white to match. It is not there in the shots before or after. (01:42:15)
Revealing mistake: A short shot from inside the bus looking forward at the moment of impact shows a wall of water fires up onto the windshield. This 'water barrel' technique is used to lessen damage and injury on many public roadways, and is used here to save the bus for use in another take - the one when it actually does hit the car a split-second of movie-time later. (01:42:15)
Revealing mistake: When the bus hits the car, the car launches into the air, propelled by a special-effects 'roll cannon'. The cylindrical slug that is fired out of the bottom of the car is seen rolling ahead of the bus toward the bottom of the screen. (01:42:15)
Continuity mistake: At the end, when Riggs is at his wife's grave, it's supposedly raining. In one shot you see Riggs' hair is dripping wet, and when you see him bend down to put the flowers on the grave in the next shot, his hair is dry, and in the next shot it's wet again. (01:44:00)
Continuity mistake: When Mel Gibson is talking about the special bullet, kept as the suicide special, he describes it as a hollow point - to do the job right. When he shows the bullet it is a full metal jacket.
Continuity mistake: In the scene where Riggs is chasing Joshua and is told by Murtagh to take a shortcut to catch Joshua, he is shown running in bare feet. After shooting at Joshua from on top of the freeway he then runs down the embankment and is shown wearing tennis shoes, but there is nowhere these shoes could have come from and he is never shown putting them on.
Continuity mistake: Director's cut (or extra scenes on Lethal Weapon 4 DVD): When Riggs is sitting there at the beginning of the movie, he is crying and looking at the picture of his wife on the right and wedding day on the left. Earlier in the movie when the picture was setting on the TV set his wife's picture was on the left and his wedding day picture was on the right. Not only that, but in at the start the pictures are in a folding frame. During the near-suicide scene they are not. [The first scene shows Riggs has damaged the frame, and says to the photo of his wife, "I'll buy you a new one." which explains the later changes.]
Continuity mistake: When the bus hits the General's car, the bus windshield (at least on the driver's side) is all smashed up as seen from the shot inside the bus. However, when the bus backs up, and in later shots of it, the windshield is undamaged.
Audio problem: In the beginning, when Murtaugh's daughter comes downstairs in the black dress the dialog is dubbed in. After the spin, she's talking but she doesn't move her mouth (even before the spin she isn't in sync). Her little sister replies and doesn't move her mouth either.
Continuity mistake: In the scene where Riggs is jumping off the bridge when chasing Mr. Joshua, first he has a rifle in his hand, his shadow on the bridge shows no rifle, when he lands he picks the rifle up off the ground and keeps running.
Factual error: In the desert shootout scene Murtagh throws what looks like an M67 "baseball" hand grenade on the ground. They wait for it to explode and Gary Busey says "it's a smoker". M8 smoke grenades look like a soda can, nothing like the baseball shape of a live M67.
Suggested correction: First, the grenade shown is more like the M61 "lemon" grenade. And there's no telling if Murtaugh/Riggs obtained a M61 based smoke grenade perhaps from a military surplus store that added the smoke effect for realism without the bang, or even a home made by Riggs grenade for this purpose, as opposed to using actual US Military M8 smoke grenades.
Factual error: When Riggs and Murtaugh are at the indoor shooting range, Riggs shoots a smiley face at long range. Every shot makes Mel Gibson blink and twitch from the bang. No expert marksman would react like that to the gunshot. Nor could his shot placement be so accurate with that reaction.
Revealing mistake: In the wide shot of the bus colliding with General McAllister's car, look at the front seat of the bus and you can see that the driver is a mannequin.
Other mistake: Towards the end, when Riggs runs up to Murtaugh just after the car explodes, Riggs is carrying a large machine gun in his right hand. He runs up to the police barricade, but the police officer won't let him by until he shows him his ID. The police officer completely ignored the fact that Riggs was holding a large gun and could have been a criminal who wanted to use it.
Continuity mistake: Their car goes round the corner and the police light falls off the roof and dangles, yet is back on the roof a second later.
Plot hole: There is no way Riggs and Murtaugh would have let Joshua kill the two officers guarding the house, if they were already waiting for him. And if they didn't get to the house first, there certainly would not have been enough time for them to reach the house and leave a message waiting for Joshua in that short space of time. So, were they waiting for him or not, and why let two cops be killed if they were?
Suggested correction: They didn't get to the house before Joshua; they showed up after he killed the two police officers. The note is in a child's handwriting, so it's more likely that Murtaugh called the family to tell them to evacuate the house, and one of his kids left the note.
Deliberate mistake: At the end of the film, two officers attempt to surround and handcuff Joshua. Using two officers to cuff someone is NEVER done for the exact reason of what ends up happening, as Joshua manages to grab a gun from one of the officers. Only one officer would have been doing the deed in the real world, but it's clear this error in being completely against police protocol had to happen so the good guys could prevail over the villain.
Continuity mistake: Towards the end before Riggs saves Roger and his daughter he is wet, but when he is running on the street his hair is absolutely dry.
