Den mörka herren hörde bara en del av det, han ville höra resten.

Snape hörde bara en del av profetian, inte hela grejen. Den mörka Herren visste det här och ville höra det hela om han saknade någon viktig information.

“My – our – one stroke of good fortune was that the eavesdropper was detected only a short way into the prophecy and thrown from the building.’

‘So he only heard –?’

‘He heard only the beginning, the part foretelling the birth of a boy in July to parents who had thrice defied Voldemort. Consequently, he could not warn his master that to attack you would be to risk transferring power to you, and marking you as his equal.”
- Harry Potter and the Order of the Phoenix, Chapter 37 (The Lost Prophecy)

Efter Harrys fortsatta överlevnad trodde den mörka herren att profetian skulle innehålla några viktiga uppgifter som skulle göra det möjligt för honom att få överhand och döda Harry.

“Voldemort tried to kill you when you were a child because of a prophecy made shortly before your birth. He knew the prophecy had been made, though he did not know its full contents. He set out to kill you when you were still a baby, believing he was fulfilling the terms of the prophecy. He discovered, to his cost, that he was mistaken, when the curse intended to kill you backfired. And so, since his return to his body, and particularly since your extraordinary escape from him last year, he has been determined to hear that prophecy in its entirety. This is the weapon he has been seeking so assiduously since his return: the knowledge of how to destroy you.”
- Harry Potter and the Order of the Phoenix, Chapter 37 (The Lost Prophecy)