When Hopkins is looking at the classifieds in Julia Niemeyer's apartment the first advert circled in red is in the last column of the newspaper, the second advert circled in red in the second newspaper is in the second column from the right. In the very next scene the circled advert is again in the last column of the newspaper even though Hopkins placed the first newspaper on the desk.
When Hopkins calls Peltz to tell him about killing Haines, Peltz is wearing a plaid sports coat with a tan shirt and brown striped tie. When Peltz arrives he is wearing a tan coat with a blue shirt and a paisley tie even though it's the same day.
Julia Niemeyer's corpse is facing Hopkins when he first opens the bedroom door. In a subsequent closeup the body has suddenly turned 90 degrees.
When Woods is walking around in the gym with his shotgun and at risk for being ambushed, he doesn't bother to chamber a shell until he has been there for several minutes.
Lesley Ann Warren chain-smokes throughout the movie but is clearly a non-smoker. She never handles the cigarette like a smoker would, constantly takes puffs without inhaling, picking up and putting the cigarette down constantly when a real smoker would hold it. It's just obvious she's not comfortable with the cigarette.
The dead body hanging in the apartment can be seen moving several times when Lloyd Hopkins discovers it.
Obvious stuntman when Hopkins jumps from the mezzanine in the school gym.
Hopkins goes to the initial murder scene by himself, even though the killer might still on the premises. Once there, he handles the doorknob, phone and other objects with his bare hands. No experienced police officer, even one who's supposed to be a bit of a loose cannon, would make such rookie mistakes.