The man who kept his daughter and their children imprisoned in a home-made dungeon warned them they would be gassed if they tried to escape, police revealed today.
Austrian Josef Fritzl ,73, who fathered seven children by raping his daughter Elisabeth, repeatedly told them they would die if they harmed him.
Police spokesman Helmut Greiner said Fritz warned gas would flow into the dingy, windowless cellar underneath his house in the town of Amstetten.
Fritzl told police about his threats during interviews and they were checking today to see if he had actually installed a device to carry them out.
They are also investigating another Fritzl claim that the reinforced door leading to the enclosure had a timer that let it be opened if he was gone for an unusually long time.
Police also said Fritzl forced his captive daughter to write a letter late last year indicating he may have been planning to release her from the cellar where she was held for 24 years.
They said DNA tests proved Elisabeth had written the letter to her family, who believed she had fled to a cult.
In it, the 42-year-old writes she wants to come home but "it's not possible yet."
"He may have had plans to end the captivity at some point," a spokesman said.
Fritzl's crimes came to light after one of Elisabeth's daughters, 19-year-old Kerstin, was admitted to hospital on April 19 suffering from an illness linked to an unidentified infection.
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 allowed Elisabeth to go to hospital, and her story emerged.
Days before Elisabeth told police of her 24 years in captivity, police had become suspicious and started investigating Fritzl, according to a police statement.
It said police decided to compare DNA samples of the hospitalised Kerstin and of Fritzl, along with family members living with him in late April, about 10 days before revealing the ordeal to the public.
Fritzl and Elisabeth were held on 26 April near the hospital where Kerstin was being treated and Elisabeth then told her story to interrogators.
Police in Upper Austria are also examining whether Fritzl was also responsible for an unsolved murder in a nearby lakeside village where his wife owned an inn and camping ground.
The bound body of 17-year-old Martina Posch was found on a shore of the Upper Austrian lake of Mondsee in 1986. Fritzl's wife owned part of an inn and camping ground on the other side of the lake at that time and he could have been in the area at the time.
Compiling a complete profile of Fritzl has been difficult because he is refusing to undergo more questioning, police say.
The other dungeon children appeared to be doing relatively well. Berthold Kepplinger, director of the clinic where they are being treated, said they were "talking a lot" with each other.
"The family is doing well under the circumstances," Dr Kepplinger said, considering they had to get accustomed to everyday conditions for others, such as daylight.
Elisabeth and her mother, who cared for the three children father Josef brought into his own apartment, were also "getting along very well," said Dr Kepplinger. He said staff was trying to create the conditions for "the best possible start into a new life."Reuse content