What aspect of this passage is common to much crime/detective fiction7

A number of potential suspects are alluded to who will be further developed later on.
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The use of dark imagery paints a sense of imminent danger around the detective.
It presents an unlikely main character who appears to be clumsy and unqualified.

The aspect common to much crime/detective fiction in this passage is the presence of potential suspects being alluded to and further developed later on. This is a common trope in crime fiction where multiple characters are introduced as possible suspects, adding to the mystery and intrigue of the story.