After partially completing his second diary entry, a hard gust of wind blew, and the diary of Severus Snape disappeared. After that, Snape heard a voice in his head saying that his diary would appear when the time was right. Severus Snape found his diary on the day he had killed Albus Percival Wulfric Brian Dumbledore. On that sad day, Snape had nothing to do, no one soul to confess his deepest thoughts with, and no one to actually to tell the truth to. Finally, the diary appeared in his hands as he was running away from Harry Potter.