Continuity mistake: During the trial when Beverly is cross-examining Mrs. Ackerman, her neighbor, she asks if those were her scissors found sticking out of Mrs. Sterner's stomach. That's not where the scissors should have been found. After stabbing Mrs. Sterner with the scissors, Beverly pulled them out and threw them at the husband twice, both times they ended up sticking in the walls, and that is where the scissors would have been found when the police arrived.
Continuity mistake: During the opening, when the fly finally lands on a coaster, Beverly Sutphin swats it quickly and removes the swatter. Cut to a close-up, and the swatter and dead fly are still there.
Continuity mistake: When Mrs. Jenson is getting ready to watch her movie Annie, she cuts a piece of the leg of lamb and puts it on a sandwich. When she sits down she takes a bite and put the sandwich back on the plate, you can see a bulge of meat on the sandwich when she takes the bite. A few minutes later when the dog starts barking after Beverly enters the house, the meat is gone.
Factual error: When Mr. Sutphin finds Beverly's things on Richard Speck, there's an envelope he mailed her, with his return address, which is wrong. It is listed as Stateville Correctional Center (which is where Speck served his time in real life): Joliet, Illinois 60434. However, SCC is located in Crest Hill, Illinois 60403.