Factual error: When the detectives are first bringing Calogero out to the street after the shooting by Sonny, an electronic siren can be heard winding down and cutting off mid-tone. Only motor-driven sirens were available on emergency vehicles during this period, and when they were turned off, they simply wound down.
Factual error: Although the movie neighborhood is meant to be 187th Street and Belmont Avenue, a NYC bus (from the old Surface Transportation System) is shown running along that street, where none ever did. In at least one scene, the sign on the bus indicates it's the 12 bus, Fordham Road from Sedgwick Avenue to City Island. Fordham Road was three blocks north of 187th Street, and never had its own bus route.