During 1589, Stumpp had one of the most lurid and famous werewolf trials of history. After being stretched on a rack, and before further torture commenced, he confessed to having practiced black magic since he was twelve years old. He claimed that the Devil had given him a magical belt or girdle, which enabled him to metamorphose into "the likeness of a greedy, devouring wolf, strong and mighty, with eyes great and large, which in the night sparkled like fire, a mouth great and wide, with most sharp and cruel teeth, a huge body, and mighty paws." Removing the belt, he said, made him transform back to his human form. No such belt was ever found after his arrest.