Josef Fritzl (born 13 April 1935) is an Austrian criminal. He held his daughter captive in a basement dungeon that he built under his house. Fritzl made his daughter write letters to him and her mother, saying she had joined a cult. During the 24 years that he had her imprisoned, Fritzl often raped his daughter, and she had seven children by him. One of the baby boys died and Fritzl burned his body. The police eventually found out about his crimes when one of the children became very sick and he took her to the hospital.