Question: Whose murders did Voldemort use to create each of the Horcruxes?
J.K. Rowling: The diary - Moaning Myrtle. The cup - Hepzibah Smith, the previous owner. The locket - a Muggle tramp. Nagini - Bertha Jorkins (Voldemort could use a wand once he regained a rudimentary body, as long as the victim was subdued). The diadem - an Albanian peasant. The ring - Tom Riddle senior.
-- Bloomsbury Live Chat (BLC)
When he found Ravenclaw’s diadem in Albania, Voldemort killed a peasant and used his or her death to turn the priceless object into a Horcrux (BLC).
- When Tom Riddle was at school he discovered the story of the diadem of Ravenclaw by flattering the ghost known as the Gray Lady. She was the daughter of founder Rowena Ravenclaw and had fled Hogwarts with the diadem, taking it with her to Albania. A man who loved her tracked her down, but when she spurned him, he stabbed her to death, then killed himself, becoming the ghost known as the Bloody Baron (DH31).
- She told Tom that she had hidden the diadem in a hollow tree in Albania, and he tracked it down there, where he also murdered an Albanian peasant to turn it into a Horcrux (HBP20, DH31).
- While talking to the Gray Lady, Harry figured out that on the night Tom reappeared as Lord Voldemort to ask Dumbledore for a job teaching Defence Against the Dark Arts, he hid the diadem somewhere in the castle (DH31).
- Harry remembered seeing the diadem it in the Room of Requirement the year before perched on a bust of an ugly Warlock (HBP24).
- Before Harry could get to the diadem Horcrux, Crabbe's Fiendfyre destroyed it (DH31).
There's an inconsistency about the creation of Voldemort's Horcruxes. Dumbledore told Harry that he only used "significant deaths" (HBP23), and that is true for the ring that belonged to Marvolo Gaunt - he used the murder of his own father, Tom Riddle. Yet for something as important as the diadem of Ravenclaw, Voldemort used an insignificant Albanian peasant who meant nothing to him. He also used a "Muggle tramp" to create the Horcrux from Slytherin's locket, which seems even more unbelievable considering the way Tom Riddle revered his ancestor Salazar Slytherin. Why would Dumbledore say that the deaths had to be significant, when actually most of them were not?