Mr Fritzl claimed his daughter ran away to join a cult
Josef Fritzl, the Austrian man accused of abusing his imprisoned daughter for 24 years, should not go to jail as he is mentally ill, his lawyer says.
Rudolf Mayer says his client should be in a psychiatric unit rather than facing a trial, which will not be fair because of press coverage of the case.
Police say Mr Fritzl, 73, incarcerated and raped his daughter Elisabeth in his cellar in Amstetten in Lower Austria.
A relative of Mr Fritzl says he was convicted of another rape in 1967.
In a television interview for the Associated Press, Mr Fritzl's sister-in-law, identified only as Christine R, describes Mr Fritzl as a tyrant and said "I believe he spent a year and half in prison" for the conviction.
Rudolf Mayer says his client should be in a psychiatric unit
Police have declined to comment on the allegations, saying records that old would have been erased under Austria's statutes of limitation.
Under Austrian law convictions can be expunged after as little as five years.
Mr Mayer has said that if, in his opinion, a psychiatric evaluation of Mr Fritzl ordered by the court does not give a proper assessment of his client he will consider ordering a separate report himself.
"In my personal opinion, Josef Fritzl is mentally ill and therefore of diminished responsibility. I believe that my client does not belong in prison but in a secure psychiatric unit," Mr Mayer told the German newspaper Bild am Sonntag.
Josef Fritzl's sister-in-law talks about the family
He added that he is "not defending a monster but a human being, even if that is hard to take for some people. I am already receiving threatening letters saying that I belong in the cellar with Mr Fritzl."
Police say Elisabeth bore her father seven children - three of whom remained incarcerated with her, never seeing daylight until they were released earlier this week.
Mr Fritzl, who is in custody, has confessed to the crime in a written statement.
He is refusing to answer any more questions, as police try to piece together conditions in the cellar - as well as the suspect's life.
Mr Fritzl's alleged crimes came to light when Elisabeth's eldest daughter Kerstin, 19, became seriously ill.
She was allowed out of the cellar and admitted to hospital in Amstetten.
Police then issued an appeal to Elisabeth Fritzl to contact them about her daughter, and later picked up Mr Fritzl and Elisabeth near the hospital.
Elisabeth and the children are now in care with the Austrian authorities, who are protecting their privacy at a psychiatric clinic.
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