Katie Pladl's death shows the irony of her biological mother's efforts to protect her from her father.

The convicted killer and father of 12 tortured and sexually abused his children for years, exerting such power that some of them murdered at his command.

Josef Fritzl imprisoned his daughter Elisabeth for 24 years in a windowless basement. When she finally emerged in 2008, the story of his sadism shocked the world. Read about this shocking case.