While planning the train robbery, the characters calculate a 20-minute window. The scene in which the robbery actually takes place runs exactly 20 minutes.
While Alain Delon's character, Commissioner Coleman, examines a crime scene, we see a brief shot of a wall covered with names, including "Jef Costello." Jef Costello was the character Delon played in Le Samouraï (1967), one of his earlier collaborations with Jean-Pierre Melville.
During filming, director Jean-Pierre Melville had a wooden cabin built above the set and often stayed inside it, refusing to speak even with the technicians and actors.
Two of Jacques Tati's children were part of the production crew. Pierre Tati was second assistant director and Sophie Tatischeff worked in the editorial department.
In a 1973 interview, Jean-Pierre Melville admitted that he would never watch A Cop (1972). He did not like his films and tried to stay away from them after production.
As in another Jean-Pierre Melville film, a woman wears nurse's clothes to help a prisoner escape: here it is Simone Signoret rather than Catherine Deneuve, in Army of Shadows (1969).