The situation at the opening of the movie is based on an incident when, as a child, author Dennis Lehane's mother severely reprimanded him for getting into a car with men who claimed to be plain-clothes policemen.
The studio executives at Warner Bros. wanted Clint Eastwood to shoot this movie in Toronto, Ontario to save money. Eastwood refused and pushed to have this movie completely shot in Boston where it is set.
When the young Dave is thrown into the backseat of the car, a man in the front passenger seat turns around and displays a bishop's ring. The book never indicates that the character was a priest, but it was added to this movie since filming took place during the priest sexual abuse scandal in the Boston archdiocese.
Michael Keaton was originally cast as Sean Devine. He had done several script readings with the rest of the principal cast, and he had been doing research for the role with the Massachusetts State Police Department, and living in Boston for several weeks. A month before principal photography was to start, Keaton and producer and director Clint Eastwood got into a huge argument, and Keaton left the project. A week later, Kevin Bacon was cast in the role.
Eli Wallach claimed that he filmed his scene in one take and without a single word of direction from Clint Eastwood, who had such confidence in his acting that merely knowing his lines would be enough.
Eli Wallach: He appears uncredited as a liquor store owner in his first movie with Clint Eastwood since Le Bon, la Brute et le Truand (1966).
Dennis Lehane: The author of the novel can be seen waving from the back of a convertible in the parade sequence.