The Ministry of Magic turned Azkaban into the main prison for wizards, fearful of angering the Dementor colony that lived there. After the Second Wizarding War, conditions improved, Dementors were ...

so he stole the passwords into Gryffindor Tower for me.... As I understand it, he took them from a boy's bedside table...." Azkaban was supposed to be the most secure prison in the Harry Potter ...