Josef Fritzl, who raped his daughter up to 3,000 times over a 24 year period after locking her up in a dungeon, planned to kill his cellar family by dipping them in an acid bath, said the Austrian's prison cell mate.

Fritzl told his cell mate, 19-year-old Patrick Jakob that he was tired of living two lives and wanted to rest in his old age. Jakob spent three months locked up with Fritzl in St Poelten jail, Austria.