Factual error: Right before Frank humiliates Dorothy for the first time, he blows out one of the gaslights in her apartment. That is never done in real life, for the same reason you would not blow out the pilot in your stove.
Factual error: When Frank comes to kill Jeffery in Dorthy's apartment he rakes the slide (cocks the gun). Then he fires in the bedroom and then rakes the slide after each shot. On a semi-automatic, as he was using, the fired bullet automatically chambers the following round and cocks the gun so there is no need to re-cock the gun with your hand. Raking the gun slide as he does in the movie would cause an unfired round to eject out the side of the gun. (01:54:00)
Factual error: When Mike's car hits Jeffrey's from behind, Jeffrey's and Sandy's heads move first forward and then backward. Physical laws, however, would have it the other way around.