Using Veritaserum, a truth potion, they learn that Barty Crouch Sr. rescued his son from Azkaban as a favour to his dying wife: the Crouch Jr. who died in Azkaban was his mother, disguised under Polyjuice Potion. Crouch Jr. was kept imprisoned at home. Winky convinced Crouch Sr. to allow Crouch Jr. to see the Quidditch World Cup, where he stole Harry's wand, escaped, and conjured the Dark Mark. Wormtail, meanwhile, had captured Bertha Jorkins, who had once seen Crouch Jr. at home and been bewitched to forget. This allowed Voldemort to discover Crouch Jr.'s whereabouts, then formulate a plan to install Crouch at Hogwarts and lead Harry to him. Crouch Sr. was imprisoned by Wormtail, and when he escaped to Hogwarts, Crouch Jr. killed him.