When he was filming the fight scene at the testimonial dinner, director Ulu Grosbard never informed the extras that there would be a fight. When it occurred, their reactions were genuine.
To prepare for his role as Detective Tom Spellacy, Robert Duvall went on the night beat with real-life Los Angeles area homicide detectives. Duvall also went on a stakeout, witnessed the administration of a lie detector test, and visited a real murder victim crime scene.
The church where the two brothers meet in the opening scene is the same church used in wedding/murder scene in both Kill Bill: Vol. 1 (2003) and Kill Bill: Vol. 2 (2004) (East Avenue G and 198th Street East, Lancaster, CA).
This was the first film that Robert De Niro did after Raging Bull (1980). He kept some of the weight that he gained for that movie, because he felt that it better fit the character, although he still had to drop fifty-five pounds (twenty-five kilograms).