(at around 1h 14 mins) After Catherine scratches Nick, drawing lines of blood, she flips him over and is on top of him, theoretically smearing that blood all over the pristine white sheets. No blood is ever visible on the bedding.
(at around 5 mins) When Nick Curran and Gus arrive outside and enter Johnny Boz's home at the start of the film, Nick's hairstyle is combed and wavy as he goes upstairs to Boz's murder scene. When Curran walks through Boz's bedroom to examine the crime, his hair is gelled and slicked back.
(at around 1h 26 mins) When the black Lotus Esprit crashes through the barricade, the high beams are off. As we see it come through the barricade from below, the high beams are on.
(at around 1h 16 mins) When Nick gets up from bed, the scratches on his back are barely visible. When you see his back reflected in the mirror when he speaks with Roxy, the marks are bright red, bloody. When he returns to bed, they're the way they were in the previous scene.
(at around 1h 14 mins) The marks from Catherine's scratches can be seen on Nick's back before she scratches him.
A police department would not let people lead investigations that they blatantly have conflicts of interest with.
The police would have requested Catherine's DNA.
After dropping off Catherine at her home, Nick orders a "double blackjack on the rocks" at a bar, but there's no ice in his drink.
(at around 25 mins) The police would have charged Catherine for smoking in an interview.
(at around 2 mins) Sharon Stone's face is clearly recognizable in the opening scene, especially in the HD version.
When Nick is reading the magazine article 'Hot Couples', the text is repeating itself over and over again to fill the page. [This is not noticeable on the VHS, DVD, and Blu Ray versions, but it can be seen on the 4K Blu ray release.]
It is obviously Sharon Stone's body in the opening scene, not Jeanne Tripplehorn's.
(At around 1 hour 14 mins) There's no refractory period between Nick Curran's first orgasm and second orgasm with Catherine Tramell, which is unusual for someone of Curran's age.
(at around 45 mins) When Nick calls up Hazel Dobkin's police record it states that she was released from San Quentin in 1965. San Quentin has been men only since 1934.
(at around 1h 12 mins) The camera is reflected in the bed posts when Catherine and Nick are in bed.
(at around 42 mins) Camera and crew reflected in Nick's sunglasses when outside Hazel Dobkins' house.
In reality the police would have simply got the court to request that Catherine Trammel provide a DNA sample, since she was the last person seen with Johnny Boz. Since her bodily fluids and skin fragments would be all over the crime scene the police would know she was having sex with Boz when he was murdered. If Trammel had refused to provide a DNA sample she would have been charged with obstruction of justice.
DNA would have shown Catherine was having sex with Johnny Boz when he was murdered.
DNA is not mentioned even though the film is set in 1992. DNA was used in a rape case in Florida in 1986, and it was used to convict Colin Pitchfork of murder in the UK in January 1988.
The police already had enough evidence to arrest Catherine at the beginning of the film.
Any evidence Nick obtained while he was suspended would have been thrown out by a court after he had become sexually involved with Trammel.
Throughout the film, several characters use the word "alibi" in a wrong sense. They use it to refer to the argument that Catherine would not have committed a crime very similar to one described in a novel of hers. But that is not what the word alibi means. It refers to a piece of evidence which shows that a suspect could not have been at the scene of a crime at the time of that crime (the literal translation of the Latin word "alibi" is "elsewhere"). The description of the ice pick murder in Catherine's novel does not prove anything of that sort.
(at around 13 mins) Beth Garner's first name is spelled "Elisabeth" on the entrance door to her office. However, when Nick looks up her driving license records (at around 1h 35 mins), the name is spelled "Elizabeth".
Even though there's no smoking allowed in the building throughout the movie we see police officers smoking inside the offices and hallways.