About 2 minutes into the film, Luther goes to Red's Bar. He opens the door and enters the bar from the street. The next scene, inside the bar, shows Luther entering the bar again from the street. The door has changed from a solid door to one with a diamond-shaped widow in it.
When Luther's daughter is reading the newspaper, the headline story about the murder, and the story about the jewelry theft have identical text, even though they are different stories. The newspaper text contains nothing about the murder or jewelry theft. In fact the story seems to be about a city council or Congressional hearing.
When Kate and Seth are outside Luther's front door, the shutters on the security door are wide open. After going through the door, the shutters are completely closed.
When McCarty is setting up, he sticks his rifle out the window and dry fires it a few times. Anyone who even glances up at the building could easily see him, which hardly seems professional.
Both Collin and McCarty affix silencers to their rifles as they take positions prior to the café meeting. Both should have been well aware that it is impossible to silence a rifle that fires a supersonic bullet. Indeed, when the rifles are fired, the shots may be clearly heard.
When Seth Frank introduces himself to Walter Sullivan, he tells him he is from Middleton County. But, there are no counties in Washington, DC, where Seth Frank is stated to work for the Police Department.
When Clint Eastwood ascends the stairs of the mansion after turning off the alarm, he passes a Gainsborough painting called "Mary, Countess Howe." This painting is actually hanging in the museum of fine arts in Houston, Texas.
The manor that Luther robs is only three stories high (clearly visible from the rows of windows on the outside) yet he walks up four flights of stairs to get to the safe in Christy Sullivan's bedroom. That's because the floors are high and there is more than one flight of stairs between two floors (at least three).
As Richmond attacks Christy Sullivan at the beginning of the movie, he rips her dress. While her dress is intact later, this may have been part of the damage control by his team.
When the Special Agents of the US Secret Service are attempting to push Kate off the cliff, the license plates on the suburban are Washington, DC Official Plates. Normally, the Secret Service would be operating a vehicle with US Government plates if it is an official vehicle or regular plates if they were undercover.
The grass at the parking lot where Kate jogs is car bumper high. If this were an actual parking lot, the grass would be trampled.
When Luther puts the VCR tape in the machine it is at the end of the tape, but he plays it without rewinding.
While Leland is making a telephone call the line is ringing, but he is still dialing numbers.
When Luther opens his safe, he doesn't make enough stops on the dial.
Both snipers are shown inserting one cartridge into their weapons. These are not singe-shot rifles. Besides, one might have to take more that one shot without having to reload each time.
After having pushed Kate off the cliff, the secret service agent's vehicle crosses path with Luther's vehicle. They are actually getting eye contact, as suggested by the cut. Now, while Luther doesn't know the agent by face, the latter one knows Luther, to be sure. He acted as sniper on him earlier. Yet the agent makes no attempt to go after his primary target. Instead he leaves, only to return to the hospital in order to attempt once more to kill Kate.
Christy starts the music with the wrong remote control. The stereo is a Bang & Olufsen Beosound 9000 but the remote she is using clearly is not a Beolink remote, which had a very distinctive design.
In the pictures of Luther's daughter with her mother, she is shown to be wearing fairly modern disposable diapers however in reality, when she was a toddler she would have been wearing cloth diapers with rubber pants; disposable diapers were a new invention in the 60s (approx when the child was that age).
When Burton and Collin are chasing Whitney through the woods, a shadow of the camera is visible in the trees behind them.
When the Special Agents of the US Secret Service are pushing Kate off the cliff, a mechanical device is seen clearly pushing the car over the cliff.
When the two bodyguards go back into the mansion to retrieve the knife, which has been accidentally dropped somewhere, they know exactly where it should be. When they don't find it, they assume Luther has it, and don't search any further.
Immediately after the secret service agents have pushed Luther's daughter off the cliff, Luther arrives on the scene and exchanges a glance with them. They see him but drive off. Considering they have spent most of the film trying to apprehend and kill him, why did they not stop and intercept Luther right there? It was a fairly deserted location and thus perfect to kill him. Instead, they go to the hospital where his daughter is recovering and continue their attempts to kill her.
When Luther breaks in the mansion, he disables the security alarm. The President, Kristy Sullivan and the secret service arrive while Luther is still inside, yet no one is suspicious of the disabled security alarm.
It is never explained why Gloria Russell, the President's chief of staff, was accompanying the President, his two body guards and his mistress since Richmond and Christy were going to spend that night together.
It is never explained in the film how McCarty, Walter Sullivan's hired assassin, finds out about the meeting at Café Alonzo, which was only arranged the day before. (In the book Burton tells the President to inform Sullivan.)