An Austrian man who held his daughter captive for 24 years and fathered her seven children repeatedly warned his captives they would be gassed if they tried to overpower him, a spokesman for investigators says.
Separately, authorities said Josef Fritzl forced his captive daughter to write a letter last year indicating he may have been planning to release her from the windowless dungeon where she lived with three of their children.
Police Colonel Franz Polzer said Elisabeth Fritzl wrote to her family, who believed she had fled to a cult, that she wants to come home but "it's not possible yet".
DNA testing on the letter proved that 42-year-old Elisabeth had written the letter, but Polzer said she was forced by her father to do so.
"He may have had plans to end the captivity at some point," Polzer told The Associated Press. "It just shows how perfectly he planned everything."
Fritzl's elaborate crime came to the attention of authorities on April 19 when one of Elisabeth's daughters, 19-year-old Kerstin, was admitted to a hospital suffering from an illness linked to an unidentified infection.
Baffled doctors then appealed on TV for Kerstin's mother to come forward because they needed information from her about her daughter's medical history. Fritzl then accompanied Elisabeth to the hospital, and her story came to light.
"It shows that he must have had a spark of humanity," Polzer said.
Police in Upper Austria are also examining whether Fritzl was also responsible for an unsolved murder in the nearby lakeside village of Mondsee two decades ago, where his wife owned an inn and camping ground.http://au.news.yahoo.com/080501/2/16p31.html?f=mv