The daughter of Josef Fritzl, the Austrian incest offender, has given evidence against her father to court authorities for the first time this week.

Fritzl, 73, a retired engineer, incarcerated and sexually abused his daughter Elisabeth, 42, in a purpose-built concrete dungeon beneath his home in the town of Amstetten for more than 24 years and fathered seven children with her. One of the children died shortly after birth and Fritzl burned its body in an incinerator.

The case was revealed on April 26 but doctors treating Elisabeth and her family have only now allowed the first questioning to take place, with her condition said to have dramatically improved after two months of intensive psychotherapy and medical care.

Elisabeth has now revealed details of her ordeal for the first time to Judge Andrea Hummer, who will try the case against her father. She was questioned only in the presence of the judge and her lawyer, while prosecutors and the legal representative of her father were able to ask questions via video-link from a separate room.

The hearing will continue into next week and possibly beyond that. Elisabeth's two oldest children, who spent their entire lives in the cellar, Kerstin 19, and Stefan, 18, will also be questioned by the court as soon as doctors give their approval.

Their testimonies will be recorded and presented to the court during the trial, expected to take place by November this year, in order to honour Elisabeth's demand that she and her children never be confronted with their father again.

Fritzl has given up on his right to follow the questioning of his family and even ask them questions, together with the prosecutor and his lawyer, via video-link.

His lawyer, Rudolf Mayer, said: “My client will definitely not attend the questioning.”

Details of the testimonies of Elisabeth Fritzl and her children will not be made known to the public. The trial, which will be scheduled as soon as prosecutors complete the charges after the testimonies of the family, is also expected to be closed to the public. Under Austrian law, a jury of eight will decide on whether Fritzl is guilty of the charges, and they will then confer with a panel of three judges to determine his sentence.

Fritzl selected three of the children to live upstairs with him and his wife Rosemarie, 68, while the other three were forced to live with their mother in the subterranean dungeon where they were born.

However, earlier this week it emerged that Fritzl could be facing only a ten-year prison term, as Austrian law, unlike British law, does not allow for cumulated convictions. That means even if Fritzl is found guilty of multiple crimes, he will only effectively serve one punishment, for the offence that carries the longest prison sentence.

Fritzl is facing potential charges of manslaughter for the newborn that died, as well as rape, coercion, deprivation of freedom and incest. But prosecutors told The Times that since the baby died in 1997, the manslaughter charges would be “extremely difficult” to prove. Even the rape charges, which carry a maximum sentence of 15 years in prison, could be impossible to probe because of a lack of forensic evidence.

It is therefore assumed that manslaughter will not be included in the charge at all, which means that the only charge that is certain to be proved in court is deprivation of freedom, a crime that can only be punished with ten years in prison under Austrian law.

Meanwhile, Elisabeth and her children Kerstin, 19, Stefan, 18, Lisa, 15, Monika, 14, Alexander 12, and Felix, five, have been returning to normal life with the help of a team of doctors and therapists. One of the daughters is said to have attended a camping excursion with her friends, while her brother Felix was being given swimming lessons by the medical staff at a pool in the hospital grounds.

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