Washington, May 6 : Dungeon dad Josef Fritzl secured the underground cellar, where he held his daughter captive for 24 years and fathered seven children with her, with eight doors, it has emerged.
Police revealed that a total of eight doors protected the underground warren of windowless rooms, the main one weighing half a tonne and having an electronic keycode known only to Fritzl.
They said that Fritzl's daughter Elisabeth and her children were locked inside a 35-metre square inner dungeon, which could only be reached through eight locked doors, reports the Mirror.
Once inside, seven more doors barred entrance to a maze of tunnels and storage rooms before leading to the spot where his secret family were held captive.
Police chief Franz Polzer said officers also discovered a second entrance to the underground den, buried in the garden of the monster's home, which he probably never used.
Police also said that Fritzl had planned to build his secret cell as early as 1978, when Elisabeth was 12.