The story of Elisabeth Fritzl, who was locked in a cellar and repeatedly raped by her father over 24 years, has stunned the world. Her father, Josef, stands accused of imprisoning Elisabeth and using her as a sex slave in an underground bunker beneath his house in the provincial Austrian town of Amstetten.

Over nearly a quarter of a century Elisabeth bore him seven children. Three of whom were kept in the cellar with her, three were taken to live upstairs with her father and his wife, while one baby was incinerated in the cellar furnace when he died a few days after birth.

This documentary examines the story so far and asks how Josef Fritzl managed to keep his horrific crimes hidden for so long.