While on the way to the airport, the driver of the van containing two reels of footage of the Liberty Parade sequence stopped at a Dunkin' Donuts, leaving the van unattended. It was stolen while he was inside, and the footage was never seen again. The crew had to return to Philadelphia just to re-shoot the entire scene, at a cost of $750,000. Cinematographer Vilmos Zsigmond was no longer available, so he was replaced by László Kovács.
John Travolta suffered from insomnia during the shoot. His lack of sleep helped him create a very moody performance and is why his character seems so downtrodden throughout the movie.
The idea of a man discovering a crime by listening to a recording is a reinterpretation of Michelangelo Antonioni's film Blow-Up (1966), but using sound instead of photographs.
Quentin Tarantino stated in an interview that this film is his favorite Brian De Palma movie. In fact, Tarantino cast John Travolta in Pulp Fiction (1994) because he liked his performance in this movie so much.
Al Pacino was director Brian De Palma's first choice for the role of Jack Terry. When he proved unavailable John Travolta was signed, prompting a suggestion from at least one studio executive to cast Olivia Newton-John, Travolta's Grease (1978) co-star, in the role of Sally (which De Palma refused).