A relative of Joseph Fritzl, the Austrian man who held his daughter captive for 24 years and fathered seven children by her, has said he was convicted of rape in 1967.
Mr Fritzl's sister-in-law, identified only as Christine R, describes him as a tyrant.
Austrian police have so far declined to comment on the allegation.
In the town of Amstetten this morning the community - still struggling to comprehend the revelations of the past week - gathered for a special mass to pray for Elisabeth Fritzl and her children.
After the service, worshippers signed a banner outside the church to show solidarity with the victims.
Elisabeth and her family are still being cared for at a psychiatric clinic. Her 19-year-old daughter meanwhile remains critically ill in hospital.
Christine R said the conviction was in 1967 and she believed Josef Fritzl had spent a year in prison.
Austrian police have declined to comment on the claim, saying such convictions can be erased from a person's record after as little as five years.
As speculation continues into what, if anything, Josef Fritzl's wife knew of his activities, her sister said they were all taken in by him.
He was a tyrant who tolerated no dissent, she said.
Today the lawyer representing him said his client should not face jail as he in mentally ill. Instead he claimed he should receive psychiatric care and not be put on trial.
