Bernadine's shirt and skirt disappear from the dressing room floor during her sex scene with Vickie.
In the beginning of the movie the detectives are examining the dead woman on the bed who is lying with her eyes open. As the camera pans up the dead body, you can notice the corpse blink right before the camera leaves her face. Worse still, the corpse has been mutilated by the killer and is not supposed to have any eyelids at all.
The bite-marks on the corpses could have been determined as most likely having been made by a female. A woman has a smaller dental structure than a man. Obviously forensics would have been on to that immediately. But the investigators search for a man.
Catherine allows Vickie, a murder suspect, into her house and even succumbs to her sexual advances.
Catherine can afford a model home on a detective salary.
Catherine never technically gave consent to Vickie for sex.
Vickie knows Catherine's first name without being told what it is.
Vickie removes Catherine gun belt without even looking to know it's there.