The Imposter is Revealed as Barty Crouch Jr.

PAGES: 682-683

After administering Veritaserum, Dumbledore, Snape, and McGonagall watch as the imposter begins to revert to his true form: Barty Crouch Jr. He confesses to everything, explaining how he escaped Azkaban, how he remained loyal to Lord Voldemort, and how he used Polyjuice Potion to impersonate Alastor Moody for the entire year.