More shocking details are emerging on the story of the Austrian father who locked his daughter in a sound-proofed basement dungeon for 24 years, raping her and fathering seven children.

New reports have said that Josef Fritzl tied his then 18-year-old daughter, Elisabeth, with a leash in the first few months of her imprisonment and have linked him with a rape in the 1960s.

And an Associated Press interview with Fritzl's sister-in-law painted a picture of a tyrannical man, who instilled fear and may have abused his wife as well.

While many Austrians are asking how Fritzl's wife, Rosemarie, did not know that her missing daughter was just underneath her feet, her sister-in-law said she knew nothing.

It is believed that Rosemarie was tricked into thinking that her daughter had run away at the age of 18, to join a cult.

The sister-in-law also said that Elisabeth had been abused since the age of 12 and had previously run away once.

Police are also investigating reports linking Fritzl to a 1967 rape of a 24-year-old nurse. Reports have also alleged that Fritzl was convicted and spent one-and-a-half years in jail.

But police cannot confirm that because Austria destroys older criminal records.

On Sunday, in an Austrian church worshippers prayed for Elisabeth and her six children, who endured an ordeal beyond rational comprehension.

"I know that the Christians here want so much to show their solidarity," a resident said.

Elisabeth and her children are currently receiving therapy for what they went through. The oldest child, whose illness brought the case to the authorities' attention, is still in hospital in critical condition.

Many Austrians are wondering how this could happen in their nation again and if their renowned emphasis on privacy has allowed incidents like this to happen specifically to their nation.

In 2006, a young woman escaped an underground dungeon in a quiet Vienna suburb where she was held for more than eight years.

Natascha Kampusch was 10 years old when she was kidnapped in Vienna on her way to school in March 1998. Her abductor, Wolfgang Priklopil, threw himself in front of a train just hours after her dramatic escape.

With reports from CTV's Genevieve Beauchemin and The Associated Press