Characters often talk around a point while the real subject of the conversation remains unsaid. The noir detective discovers darkness everywhere, finds it to be life's ruling principle, and learns that even the rich and privileged are usually no better than the poor and deprived. In the battle between good and evil, the greater strength is wielded by the latter. This fictional world is not ordered by poetic justice but by an amoral determinism. People are inherently evil and self-centered.
Death comes unexpectedly to all.
Chance, not intention, governs human experience. Any tracing of crime to its source is thus insignificant, a triumph not o virtue but of the detective's relentlessness and cunning. The bleak American where the private dick practices his profession holds out no real hope for a restoration of order and justice.