The elements are all here: the inky blacks, the use of existing light sources, the transformation of locations, and the keeping of characters in the dark. Alton also foregrounds what the exaggerated style and technological changes allow that previously was not possible:
Equally interesting, however, are the less flashy choices, like the contrast in exposure of foreground and background subjects.
The visual choices mark a departure from the generic material, which adheres slavishly to the pseudo-documentary formula that Fox developed with the Henry Hathaway institution trilogy (House on 92nd Street, 13 Rue Madeleine, and Call Northside 777). There is the Reed Hadley-esque voiceover narration (with excessively expository copy written for it). The opening pan shot in demonstrative manner.
But where Hathaway's DP, Norbert Brodine developed a look that at times mimicked newsreel and 16mm film and at other instances drew inspiration from them for a new realist style. Alton's work, however, operates with a looser and more expressionistic conception of "realism."
There is a case that the semi-documentary style became transformed into a generalized realism, but here the narrative exhibits a schizophrenic relationship between the Fox/Hathaway template and the sadistic-experiential approach of the Marlowe-influenced detective noirs.