The film's original title during shooting was "The Janitor Can't Dance", which is the title that both Peter Yates and Steve Tesich liked, but 20th Century Fox forced them to change the title during post-production, at first to The Janitor (the U.K. title for the film) and finally to Eyewitness, a title Yates to this day still doesn't like.
Sigourney Weaver's character was based on an infatuation that Steve Tesich had with a Washington, D.C. anchorwoman, in which he recorded her broadcasts and had pictures of her like William Hurt's character had in the film for Weaver. The anchorwoman in question, was brought in by Peter Yates for technical support on the set, to make Weaver's character more believable.
According to director Peter Yates, the script for the film was a hybrid of two screenplays that Steve Tesich had written and had gotten nowhere with either one. It was Yates who suggested that he combine the two scripts, Tesich originally balked at the idea, but finally gave in and this script was formed. Yates also said Tesich had trouble coming up with unusual plot twists because he cares more about character than plot when he writes.
A novelization of the film was authored by John Minahan, and published as a book tie-in with the movie in 1981. The novel's dust-jacket cover featured a surreal photo of the likeness of a bespectacled William Hurt against a black background, with his right eye bleeding a large tear of blood. The blurb read: "A Mystery by John Minahan. Based on a screenplay written by Steve Tesich. Now a major movie thriller from 20th Century Fox".
Second of three movie collaborations of Steve Tesich and Peter Yates. The first had been the Oscar winning Breaking Away (1979), where Tesich had won the Best Original Screenplay Academy Award, and the third and final film was Eleni (1985).
The climax of the picture takes place in a riding-stable where the horses 'live' upstairs and come and go via a series of ramps: this was clearly filmed at (or on interior-recreations of) the Claremont stables, close to Central Park ,one of the last of its kind in central New York City and which is now sadly extinct.