Years later, Sigourney Weaver would state that she was most proud of her work in this film. She worked hard to portray the mindset of an agoraphobic, and has regretted that the movie was lost in a shuffle of thrillers at the time and is not better remembered.
The trivia items below may give away important plot points.
In the climactic bathroom reenactment scene, Sigourney Weaver actually spat in William McNamara's face without his prior knowledge from rehearsals. The reaction of anger and shock in his face is quite real due to his surprise.
In 1995, due to the recent attack on two girls; of which one died, Copycat was banned in Abbotsford, B.C. Canada cinemas - many other lower mainland theaters followed suit. The similarities between the films Peter Foley and the real life "Abbotsford Killer," Terry Driver were enough for local law enforcement to grow concerned about fueling Driver, or panicking the public.
Serial killer Peter Foley, although not yet identified to the audience, appears in two early scenes in the film. He's sitting in Dr. Hudson's lecture audience and is also in the police station after the "Boston Strangler" murder and says "Hi!" to Nicoletti.
An original ending was shot and shown to test audiences where Inspector M.J. Monahan (Holly Hunter) was kidnapped instead of Helen Hudson (Sigourney Weaver) by Peter Foley (William McNamara), and taken to the school for Helen to rescue. This didn't play well for test audiences given Helen's severe case of agoraphobia.
An early version of the script had a vastly different finale. Peter Foley would capture Helen and hold her in the university where he reveals that he was a disgruntled former student of hers. This final scene would take place in an auditorium where Foley would give a lecture to Helen (complete with a slide projector) therefore reciprocating the opening sequence. This ending was meant to give more personal motives for Peter to specifically target Helen. Although this climax was scrapped there is still a trace of this abandoned subplot. In the beginning of the film Helen needs some young volunteers for her lecture to stand up for the audience to see. Peter Foley appears among the crowd, hinting that he could possibly be a former student of the lecturer.