Emotionally bruised and fearful of the world, the family of Josef Fritzl will shelter behind the high walls of a psychiatric clinic this week to escape the publicity surrounding the trial of their notorious father.

Mr Fritzl is accused of imprisoning his daughter, Elisabeth, for 24 years, locked in a windowless cellar, raping her on average three times a week, fathering seven children by her and allowing one of them to die. The 74-year-old engineer denies murdering the baby. He says that he is not guilty of enslaving the family and is expected to argue in court that he was in some respects a good father to the children whom he entombed in his specially constructed bunker.

The trial ranks as one of the most extraordinary in modern Austrian history, overshadowing even the case of Natasha Kampusch, a schoolgirl who was held for more than eight years in an underground dungeon in a dormitory suburb of Vienna.

The focus today will be on Mr Fritzl. The engineer, who has been under pretrial arrest for almost a year, is expected to express regret for the suffering of his family but will argue that he locked up Elisabeth – 18 at the time – to prevent her doing harm to herself. The prosecution indictment, extracts of which were published in the Austrian magazine News, paints a less charitable picture.

The extracts say that initially Ms Fritzl was chained to an iron pole behind her bed, making it impossible to visit the lavatory Mr Fritzl had installed in the cellar. After two days he had switched the chains so that they hung in front of her, allowing her more movement. This, and other graphic detail was provided to the prosecutor by her in 11 hours of recorded testimony. The tape will be shown to the judge, the eight jurors and Mr Fritzl who will be given the chance to reply to her accusations.

Elisabeth Fritzl, now 43, has been given a new identity and a new home in a different region of Austria, together with her youngest child, aged 6. Ms Fritzl has recovered enough to take her driving test and is in regular contact with her other children. Her youngest child is said to be doing well. The two older children from the basement - aged 19 and 20 - are still receiving intensive therapy: they grew into adulthood in a world without sunlight or outside human contact. This has given them disabilities - a stoop, restricted spatial awareness, rotting teeth and gums, skin problems, weak immunity - and, socially, they find it difficult to communicate. Speech therapists have been helping them to shed their special, very restricted “downstairs” language.

Together in the clinic, shielded from the publicity surrounding the five day trial, will be Ms Frizl’s three other children, aged 16, 15 and 13. These three children were removed from the bunker by Mr Fritzl soon after birth and were brought up in the upstairs section of the house. They are said to be well adjusted, registering good marks at school, attending music lessons and playing sport.

Ms Frizl’s seventh child died soon after birth in 1996. This forms the basis of the murder charge against her father. News quotes her testimony to the police: “A few hours later [after the birth], the child began to suffer breathing problems, his skin turned blue and his legs started to stiffen. Instead of securing medical assistance, the accused said to his daughter. ‘What will be will be’.” The baby died two days later on May 1, 1996. His body was burnt in the house stove, his ashes scattered in the garden by Mr Fritzl.

This incident is likely to be the most contentious. Mr Fritzl has told his defence lawyer, Rupert Mayer, that he is determined not to go down in history as a madman or a murderer.

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