In the sheriff's office, there are some shots of the bulletin board in the background. On the board is the FBI's Wanted Poster for Frank Morris, following his escape from USP Alcatraz. The Alcatraz escape took place in June of 1962, sixteen years after the events in the film.
Several times in the movie when we see a close-up of the cops driving in their car, you can see rows of houses behind them out the back window of their car, but in the immediate next wide angle shot they're out in the wooded countryside, with no houses anywhere in sight
At the beginning of the movie a graphic is put onto the screen to draw attention to the fictional date of the first attack. The graphic reads, "SUNDAY, MARCH 3". Later, as a lead-in to the second crime, the graphic, "SATURDAY, MARCH 24" appears on the screen. The narrator's voice adds, "Now, it is a rainy Saturday night, March 24, 1946, 21 days after the attack on lover's lane." 21 days from March 3 would indeed be March 24, but it also would be, and was, a Sunday, just as March 3 was. The second graphic and the narrator's script were incorrect.
At the very beginning, during the quick wedding scene, the extra that plays the now husband is obviously waiting for his cue to come out of the church, as he's looking down with a serious expression, while everybody else is at least smiling or doing something to act like it was a wedding.
When Peggy and Roy are about to be attacked, as they're leaving in their car from the Spring Lake Park area, Peggy puts her arm around Roy. The actor playing killer is supposed to emerge from the driver's window. You can notice that the actress playing Peggy widen her eyes and looks quickly to the window, but sees nothing. Probably she (or the actor playing the killer) missed the cue, because she then keeps looking at the window as if she was waiting for someone to finally emerge from the window.