What is peculiar about the murders in Edgar Allan Poe's story "The Murders in the Rue Morgue"?
The murders were peculiar because circumstantial evidence at the scene of the murders offered no clues as to how the murders had been committed.
For example, Madame L'Espanaye and Mademoiselle Camille L'Espanaye lived very private lives; by all indications, they admitted no close acquaintances into their lives. How then, could they have been murdered in such horrific ways? Additionally, both the neighbors and the police had to force their way into the house with a crowbar. Once inside, their rush to the fourth floor led to the discovery of an apartment that was locked from the inside. Meanwhile, witnesses claimed to have heard two voices at the time of the murders. One was reportedly that of a Frenchman, and the other of a foreigner speaking an indecipherable language of some sort, perhaps Italian, German, Russian, or even Spanish (from the viewpoint of the witnesses).
To make matters more peculiar, the immediate evidence at the crime scene offered no clues as to how the apartment had been breached. The shutters at the front of the house were always closed, and those in the back were closed at the time of the murders. There were no secret passageways the murderer could have escaped through even as the police breached the house. Additionally, the chimneys were too narrow to admit complete passage for a human body; Mademoiselle L'Espanaye's body, was after all, only stuffed partway up the chimney. Also, a trap-door on the roof had been securely nailed shut for many years.
Meanwhile, there were two bags containing nearly four thousand francs in gold left intact at the crime scene; therefore, a robbery motive could not be ascribed to the murderer. So, what was peculiar about the murders was the fact that circumstantial evidence at the crime scene appeared to offer no clues regarding the possible motives for the murders nor evidence for how the apartment had been breached.
It was only later, with Dupin's estimation that the tufts of hair he found clutched between Madame L'Espanaye's fingers were not of human origin, that the investigators began to make headway in their analysis.
The murders were peculiar because of the grotesqueness of them. The older woman was found outside, head nearly severed completely off, and body horribly beaten. The younger woman was found strangled to death and shoved up a chimney. She was so far up it that it took a few men to free her body implying that whomever killed the women had considerable strength. The weirdest part was the fact these murders were committed when the house was locked up from the inside.