A hand-held camera was used in many scenes to give a "live action" feel to those sequences. This was extremely rare in feature films of the time.
Director Nicholas Ray and screenwriter A.I. Bezzerides fully researched police force daily life and procedure in preparation, including riding with detectives in Boston's South End.
(At around 30 minutes): When Jim Wilson is driving upstate, the incidental music heard was also used eight years later by Bernard Herrmann in North by Northwest (1959).
Jim Wilson, Robert Ryan's character, is supposed to be a former football star. In real life, Ryan was a champion boxer at Dartmouth College.
A.I. Bezzerides: This movie's screenwriter as the man sitting in the booth at the bar who offers Jim Wilson a veiled bribe, a winning horse ticket.