Factual error: A headline from the Pantagraph (an Illinois newspaper) dated 19 December 2001, is shown in big letters to read, "Latest Florida recount shows Gore won election." In fact, no edition of the Pentagraph has ever featured an article that claimed this. The only time those words appeared in that newspaper was in small print over a letter to the editor dated 5 December 2001.
Deliberate mistake: After the killer nails Shannon to the ceiling, he apparently has time to remove all the nails from the wall where he originally shot her, spackle, paint and clean up all the blood before the police arrive and examine the apartment.
Other mistake: In the beginning of the film, letters on the screen describe the lady as the "Musican's Wife" It should be "Musician's Wife. "Musician's" is misspelled.
Factual error: When Trevor is struck by the VW Beetle, not only is he not thrown forward along the Beetle's path, he actually lands well behind the point of impact - more than half the length of the parked van. He doesn't bounce off another object that changes his direction. He's just thrown up, then falls rearward above the car. (01:08:35)
Factual error: A murder investigation would not be handled by a Detective Constable (he says he's in charge). Detective Chief Inspector is the usual minimum rank for a senior investigating officer, and such a high profile murder investigation is likely to be under a higher ranking senior officer.
Continuity mistake: Simon gets groceries, carries them home in two bags, and is then in the hallway without any groceries. It is never clear that he sets them down. (01:20:35 - 01:21:40)
Continuity mistake: Mariska Hargitay's necklace disappears and re-appears during court. (01:10:25 - 01:11:30)
Other mistake: The DVD release was created with a "pseudo widescreen" as various scenes cut off major action. The most obvious is in the beginning of the film when the main character meets the crazy girl. Her head is framed bottom right but the widescreen completely cuts off the crazy girl's head. This can be explained by the enormous aspect ratio of the original film, which is bigger than standard (USA) widescreen, that or a bad transfer.