Because it was Poe's first tale of ratiocination, "The Murders in the Rue Morgue" introduces more basic features of detective fiction than any of Poe's other short stories. Among these basic features are three central ideas: (1) the murder occurs in a locked room from which there is no apparent egress. In later detective fiction, this idea is expanded (though essentially retained) and is used when the author sets the scene of the murder in a closed environment — that is, on a train, where the murderer is included among the passengers; on an island, where the murderer must logically still be there; or on an estate, where the murderer has to be among the people in the house. (In this particular story, with there being no way for the murderer to escape, the police are completely baffled.); (2) motive, access, and other surface evidence points to an innocent person. Frequently in detective fiction, the amateur detective is drawn into the case because a friend or acquaintance has been falsely accused, as is Le Bon (Adolphe de Bon), who "once rendered me a service for which I am not ungrateful." Thus, M. Dupin is drawn into the case because of an obligation to the accused; (3) the detective uses some sort of unexpected means to produce the solution. We have noted above that all of the clues should be present but, nevertheless, the appeal of detective fiction lies in the unexpected solution, which becomes logical only in retrospect.
Two aphorisms concerning detective fiction today are also presented for the first time in this story of Poe's. First, the truth is what remains after the impossible has been determined — no matter how improbable that truth may seem. That is, the police determine or surmise that there was no possible egress from the room of the murdered women. The door was locked from within, and all the windows were securely locked. Second, the more apparently difficult the case is and the more out of the ordinary the case is, the more easily, ironically, the case can be solved — by the key detective. For example, the problem in "The Murders in the Rue Morgue" that has the police so stumped is simply how can a nonrational, inhuman being break through the bounds of law, custom, and civilized order and commit such a gruesome and horrible atrocity on two well-protected women? The police cannot bring themselves to conclude that a "human" could possibly do this; the house is built in such a way as to protect it from the very acts which were committed there. The murders can only be solved, logically, when a person is able to place his human mind into conformity with a non-human mind and with the irrational acts of a beast.
Consequently, we then have the superiority of the intuitive and brilliant detective, measured against the police as he infers possibilities and probabilities and observes the scene from the inferences due to the single-mindedness and limited viewpoint of the police.
The title of the story is straightforward — that is, the murders take place in the street (the Rue) of the Morgue. In the opening section of the story, Poe offers some of the views expressed above about the need of the detective to be observant (more than the ordinary person), and, furthermore, he must know what to observe. The most casual movement or expression can often reveal more than the magnifying glass which M. Dupin never uses, even though the police constantly rely on one to help them solve crimes. And also too, the superlative detective must be able to make the proper inferences from the things he observes. Here is where ingenuity becomes the most important aspect in solving a crime.
The narrator first met Monsieur C. Auguste Dupin when they were looking for a rare volume in a library; shortly, therefore, they became friends and shared an old house together. In later detective fiction, this convention is repeated; the brilliant detective and his sidekick will often share the same living abode. The narrator then gives us an example of M. Dupin's brilliant analytical ability. Strolling along the street one night, the narrator is thinking about a certain actor, and suddenly M. Dupin answers without the narrator's ever having asked anything. Then M. Dupin explains how through the logic of their previous conversation and by observing certain actions in his friend's movements, he was able to deduce at what point his friend had come to a certain conclusion.
Not long after this, there is an announcement in the paper of two "extraordinary murders." One night at three A.M., "eight or ten" neighbors were all aroused from sleep by a "succession of terrific shrieks" from the fourth floor of the apartments of Madame L'Espanaye and her daughter, Mademoiselle Camille. It took the crowd some time to break into the heavily locked gates and doors and, after hurrying up to the first landing, they all heard two voices. Then there was silence. When the fourth story was reached, and they entered the apartment, they found it in wild disorder.
Thus, we are given the bare facts of the murder. The old woman had "thick tresses" of her hair pulled out, her throat was cut so deeply across that when the police picked up the body, the head fell off.
Furthermore, the woman was completely covered with bruises, so terribly that the police assume that she was bludgeoned badly before her head was almost severed. The body itself was found lying in the courtyard four flights down from the woman's apartment, and it is impossible to determine how the body got into the courtyard because the room was completely locked from within.
Her daughter was choked to death, apparently, by the hands of an extremely powerful man, and she was stuffed up the chimney, head downward. It would have taken super-human strength to have put her there because it took such violents tugs to remove her.
The newspaper recounts how the old woman had just withdrawn 4,000 francs in gold from her bank; unaccountably, the two bags of money were found in the middle of the room, which was totally torn apart. The men who entered the apartment were all interviewed by the police, and all of the witnesses agree on one matter: There were two voices — one was the deep voice of a Frenchman and the other was a shriller, higher voice, but no one who heard that voice could identify the accent conclusively.
The physician and the surgeon both agree that Mademoiselle Camille was "throttled to death" and that "the corpse of the mother was horribly mutilated." All the bones of the old woman's leg and arm were shattered and many other bones (ribs included) were splintered. It is concluded that some kind of heavy club was used on her.
Because an acquaintance of M. Dupin is accused of the murders, M. Dupin receives permission to investigate the environs, a setting which is extremely intriguing since the newspapers report that the crime seems impossible to solve because there could be no way for a murderer to escape from the locked, enclosed apartment.
M. Dupin then begins his now-famous method of ratiocination. He maintains that one should not ask "what has occurred," but, instead, "what has occurred that has never occurred before." He maintains that the solution of the mystery is in direct ratio to its apparent insolubility, according to the police. He announces to his friend, the narrator, that he is waiting on confirmation of his solution; he expects a person to arrive momentarily to confirm his theory.
M. Dupin then points out to the narrator some of the obvious things that the police have overlooked. Among the witnesses who heard the two voices were an Italian, an Englishman, a Spaniard, a Hollander, and a Frenchman. Each one thought that the shrill voice they all heard was the voice of a foreigner, but none agreed on the nationality; furthermore, the Englishman thought it belonged to a German, but he does not understand German, the Spaniard thought it to be English, but he does not understand English, the Italian believed it to be Russian, but he does not understand Russian, and so on in every case. No person can identify the nationality of the shrill voice. And whereas they all agree that the deep French voice uttered discernible words, such as mon Dieu (my God) and sacre and diable, the shrill voice uttered no discernible words — only sounds.
As to the matter of egress from the room being impossible, the police reject the notion because of its impossibility. M. Dupin, however, says that he will show that "these apparent 'impossibilities' are, in reality," possible. Using this logic, he discovers that the locked windows have a spring in them that, once pressed, can be opened. Furthermore, since the police abandoned further examination of the windows after they saw that they were nailed down, M. Dupin decided to examine the nails. He found a nail in one window to be broken off just at the shaft so that it only appeared to be nailed shut; the nail separated when the window was open. Thus someone could have entered by the open window and closed it upon leaving, thereby springing the spring closed and making it appear as though it were nailed shut since the two parts of the nail met again after the window was closed.
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.
When the sailor arrives for the Ourang-Outang, M. Dupin pulls out his pistol, quickly locks the door, and quietly asks the sailor to give him "all the information in your power about these murders in the Rue Morgue." He assures the sailor that he knows that the sailor is innocent, but that an innocent man is being accused of the murders. The sailor then tells how he acquired an Ourang-Outang in Borneo and brought it back with the intent of selling it. One night, however, he came home late and found that the animal had escaped from the closet where he had kept it and was in the sailor's bedroom. Furthermore, the animal had a razor in its hand (it had apparently often watched the sailor shave). In fright, the sailor reached for his whip to drive the animal back into the closet, but it sprang through the open door and disappeared down a street. The sailor followed and watched it climb up the lightning rod to a lighted window, swing through the shutters and into an open bedroom. The sailor, accustomed to climbing ropes, climbed up, and since he could not swing, as did the Ourang-Outang, he was forced to watch as the animal, in frenzy, began slashing about with the razor. The screams were heard throughout the neighborhood. The sailor watched as the animal cut Madame L'Espanaye's throat and yanked out handfuls of her hair. Then, seeing blood, the animal became inflamed into a frenzy. It "seized . . . the corpse of Mademoiselle Camille and thrust it up the chimney . . . then . . . it immediately hurled [the old woman] through the window."
Thus, the words which the neighbors heard were the horrified exclamations of the sailor outside the window, and the other shrill "sounds" were the "jabberings of the brute," who escaped just as the door was being battered down by the neighbors.
When M. Dupin carries his report to the Prefect of Police, we read that it is difficult for the Prefect to conceal his chagrin "at the turn which the affairs had taken." As has now become traditional at the end of the detective novel, the police accept Dupin's solution to the murder — which they were incapable of solving. But instead of being grateful, there is, as was noted, a sense of resentment.
In conclusion, M. Dupin is actually a representative of a man who has a pure poetic intuition bordering on omniscience. He virtually "dreams" his solutions. His logical method is to identify his own intellect with that of another and thereby divine what another person must think or do. In the first part of the story, M. Dupin can so completely identify with the thoughts of others that he often answers questions before they are even asked; it is as though he were gifted with extrasensory perception. In this story, however, there is no human person for his intellect to identify with; therefore, since he encounters what seems impossible, he begins to look for a possible equation. Since it was impossible for a human being to commit the murders, M. Dupin begins to look for other sources. By this method of ratiocination and intuitive perception, he is able to solve a mystifying problem that no one else is able to solve. In this way, he becomes the first in a series of brilliant, eccentric detectives who can solve difficult murders that baffle everyone else.