When they observed the outside of the building, the police looked up at only one angle and decided that no one could possibly climb up the outside walls; M. Dupin, however, notices that if the shutters were open, a person or thing of great agility could conceivably hop from the lightning rod to the shutter of the window, thereby gaining ingress and egress to the apartment and still giving the appearance of its being impossible.
Additionally in his investigations, M. Dupin notices that no human being could kill with such ferocity and brutality — no human being possesses such strength. Thus his intuitive and analytical mind now must conceive of a murderer who has astounding agility, superhuman strength, a brutal and inhuman ferocity, and, moreover, he must explain a murder (a butchery) without a motive — a grotesque "horror absolutely alien from humanity" and a "voice foreign to all ears and devoid of any distinct syllabifications." These clues alone should allow the careful reader to venture an educated guess as to the nature of the perpetrator of the crime. Most readers, however, are like the narrator and will need even further clues. These M. Dupin provides next. He shows the narrator a "little tuft" of hair that was removed from the rigidly clutched fingers of Madame L'Espanaye, a detail which the police overlooked. Even the narrator now recognizes that this is not human hair. Similarly, after drawing a diagram of the size and shape of the hand that killed Mademoiselle Camille, the narrator realizes that it was no human hand that killed the young woman.
M. Dupin then explains to his friend, the narrator, that the handprint was identical in size to the paw of an Ourang-Outang. Furthermore, he has advertised for the owner to come and pick up his animal, saying that it was found in a wooded area far from the scene of the murders, so as not to arouse the owner's suspicion. Furthermore, he feels sure that the animal belongs to a sailor because at the foot of the lightning rod, he found a ribbon, knotted in a peculiar way which only Maltese sailors wear.
