In Slughorn's memory, we see Slughorn tell Tom Riddle that Horcruxes are a banned subject at Hogwarts and that Dumbledore is particularly fierce about it.5 Later on, when Hermione spirits Secrets of the Darkest Arts6 out of Dumbledore's office, she finds it is still a library book. Surely Dumbledore's banning this book from Hogwarts library would not stop Tom Riddle from finding out any available information about Horcruxes. Could Voldemort have found information in the Room of Hidden Things, a treasure trove of "banned or graffitied or stolen" 7 books, which he believed he alone knew about?8 Tom Riddle's explorations of Hogwarts also led him to the Chamber of Secrets and the basilisk within by mid-June of 1943, exactly fifty years before Harry's second year at Hogwarts.9 It is then, in his fifth year,10 that Tom Riddle puts "a piece of his sixteen year old self into the diary." 11 Perhaps it was then when Dumbledore, alarmed at Moaning Myrtle's death, and suspecting Tom Riddle's bullying involvement, removed Secrets of the Darkest Arts from the Hogwarts library.

In Slughorn's retrieved memory, Tom Riddle asks about Horcruxes, saying, "Wouldn't it be better, make you stronger, to have your soul in more pieces? [¦] isn't seven the most powerfully magical number, wouldn't seven’?" 12 But during that incident, Tom Riddle is already wearing his uncle Morfin's ring, proof he killed his grandparents and father in the summer of 1944, and this ring would become his second Horcrux. This was a full fifty years before the creation of Voldemort's last Horcrux, the snake Nagini, Bertha Jorkin's death, Harry's dream of Frank Bryce's murder13 and Voldemort's later rebirthing. So Voldemort's teenage plan to split his soul in seven pieces took fifty-two years to come to fruition, when he made the Naginicrux from Bertha Jorkins' death.

Before Tom Riddle leaves Hogwarts, he charms the whereabouts of the Ravenclaw diadem from Helena Ravenclaw, the Grey Lady, and afterwards, as a buyer for Borgin and Burkes, he also wins the confidence of a valued customer, Hepzibah Smith. Hepzibah shows him two treasured Hogwarts founders' items: Helga Hufflepuff's cup and Slytherin's locket. Hepzibah's murder, after which Voldemort fled, accounts for the creation of the cup Horcrux, but he may not have made Slytherin's locket into a Horcrux until years later.

Voldemort's return to Hogwarts ten years after Hepzibah's death, to apply for the vacant Defense Against the Dark Arts position, gives him the chance to hide the Diadem, already a Horcrux, in the Room of Hidden Things, where it remains unnoticed for at least three decades. But Voldemort doesn't require Kreacher or his new follower, Regulus Black, to put the Locketcrux into the basin in the cave until 1979.14 On Halloween of 1981, it can be assumed that Bellatrix Lestrange already has the Cupcrux in her vault at Gringotts, Lucius Malfoy has the Diarycrux at Malfoy Manor, the Ringcrux is buried in the Gaunt hovel, and the Diademcrux is in the Room of Requirement. However, the Locketcrux is now at Number Twelve Grimmauld Place, under Kreacher's watchful eye.

The failure of Voldemort's venture to use Quirrell to steal the Philosopher's Stone to regenerate, during Harry's first year at Hogwarts, ushers in Lucius Malfoy's imprudent ploy to use Tom Riddle's diary, not knowing it is a Horcrux. The Malfoys want to disrupt Dumbledore's tenure as headmaster of Hogwarts and stop Arthur Weasley's Muggle Protection Law from unearthing such a dangerous item in their possession. So, during a fracas with Arthur Weasley at Gilderoy Lockhart's book signing event, Lucius leaves the Diarycrux inside Ginny's second-hand Transfiguration textbook. It is the destruction of this Horcrux that betrays the existence of others made in order to ensure Voldemort's survival.