AMSTETTEN, Austria (CNN) -- Josef Fritzl's wife did not know her daughter was held captive in their basement for decades because she had been trained not to ask questions under Fritzl's tyrannical rule of the household, Fritzl's sister-in-law said.

Josef Fritzl admitted to authorities he raped his daughter and fathered her children.

"He was such a tyrant," said the woman identified only as Christine R. in a Saturday interview conducted and translated by the Associated Press.

"He tolerated no dissent," Christine R. added.

"Listen, if I was scared myself -- I was scared of him at a family party and I did not feel confident to say anything in any form that could possibly offend him -- then you can imagine how it was for a woman who spent so many years with him."

In the televised interview, Christine R. added detail to the bizarre story of 73-year-old Fritzl who was recently arrested and confessed to holding his daughter captive in a dungeon under the home for decades, repeatedly raping her and fathering seven kids -- with six of them surviving.

Christine R. also said Fritzl committed an unrelated rape in 1967, served 18 months in prison for that crime and that her sister continued to stay married to him in a desperate attempt to keep their family together.

Recent media reports also claimed Fritzl had been convicted of rape. Austrian police have said they are looking into the claims.

The horrifying story has shocked many locally and across the world. On Sunday, members of the Amstetten religious community held a Mass to remember Fritzl's family. After the Mass, members of the church signed a banner outside a church in support of the victims.

The story of the family's imprisonment began to unravel two weeks ago, when Fritzl's daughter, Kerstin Fritzl, fell seriously ill with convulsions and was hospitalized.

The couple adopted three of the children who Josef said were left on their doorstep as infants by his runaway daughter.

In the interview Christine R. said her sister, Rosemarie, truly thought that her daughter had ran away to join a cult.

"She never believed him being capable of it," said Christine R. "We were all taken in by him and believed that she (referring to Elizabeth), was in a cult and that she wouldn't come out."

It may have been Fritzl's strict rule over the household that made it possible for him to keep his gruesome secret hidden for so long, Christine R. said.

The unspeakable ordeal has taken a toll on the whole family, Christine R. said, stating that she spoke to her sister on the phone recenly.

"Five or six days after Kerstin went to the hospital I called my sister and asked her how the girl was doing," Christine R. said. "She said that she herself was doing badly, and the girl herself was doing badly and she wished with all of her heart that the girl would pull through."

Fritzl is being held in police custody. He has yet to be charged, but he can be held by police for 14 days without formal charges while the investigation is under way. That amount of time can be extended by a judge.

2008 CNN.com

May 4, 2008