Final answer:
The author does not reveal the murderer's identity through Dupin to create suspense and mystery, engaging the reader in the story.
Step-by-step explanation:
The reason the author does not have Dupin tell the narrator who he thinks the murderer is at this point is b) The author wants to create suspense and mystery.
In detective fiction, particularly in stories like those written by Poe featuring the analytical prowess of C. Auguste Dupin, withholding the identity of the perpetrator heightens the tension and engages the reader's own deductive skills.
As the plot unfolds, readers are encouraged to piece together the clues alongside the narrator, fostering a sense of involvement in the narrative that would be diminished if Dupin disclosed his suspicions too early.