I'd say an important element of the noir era is the moral confusion - the films are in black and white, but the issues of good and evil aren't.

Robert Mitchum in the Night of the Hunter is almost too much of a cartoon baddie - there is no ambiguity about him, he is evil personified. moose malloy in the Farewell My Lovely (another pursuer) is quite as brutal, but also strangely pathetic.

Similarly the Chandler detctives seem almost too morally upright for these films. The fact that they are knowing and expect the law and its factors to be corrupt is the only thing that makes them fit into this seedy world.

Bogart seems much more at one with the noir form in In a Lonely place, when his violent outburst at the start of the film is shocking to the audience.