Elisabeth, 42, and the three of her children who had been confined with her were being cared for this weekend at a sanatorium not far from Amstetten. Reports that doctors had built them a "dark sanctuary" as a refuge from reality have been denied and ascribed to the overfertile imagination of a British reporter.

Indeed, her two sons, Felix, 5, and Stefan, his 18-year-old brother, were thrilled by each new experience of "upstairs" life, according to doctors, be it the sound of a helicopter or a glimpse of the moon. They are far from normal, however. Felix prefers to crawl, even though he can walk upright if he wants to, and Stefan walks with a stoop after being confined for so long in the low-ceilinged cellar. Describing what sounded like a fantasy from the Brothers Grimm, police said the boys use "animal" sounds that baffle psychologists.

Their sister, Kerstin, 19, has suffered the most from imprisonment. Yesterday she was still in an artificially induced coma and attached to a dialysis machine, reportedly suffering from an acute, life-threatening failure of her auto-immune system.

Three of Elisabeth's other children - Alexander, now 12, Monika, 14, and Lisa, 15 - were sent upstairs shortly after they were born to be brought up by Rosemarie. Described by townsfolk as polite and well-adjusted, they are now having to get used to the sudden appearance of their strange siblings. How much they have been told is not known, but at some point - even in Austria - they will have to learn of the crime that envelops them. How will they react to the knowledge that Alexander had a twin who died three days after his birth, and that his body was burnt by Fritzl?

The six other children that Fritzl had with Rosemarie have long since grown up and left home. Two of them, Harald, 44, and Doris, 35, have been helping the police.

In the village of Mitterkirchen im Machland on Thursday, Harald could be seen in the upstairs window of his orange-painted cottage not far from the banks of the Danube. A woman who identified herself as his wife shouted at a visitor to "leave us in peace".

Several hundred kilometres away in the mountainous province of Stiria, Doris's husband appeared at the door of their comfortable villa to deny any knowledge of wrongdoing. He refused to offer any opinion of his notorious father-in-law before slamming the door.

The two sides of a country that gave the world Mozart and Hitler are well reflected in Amstetten. Giant plastic pears adorn its roundabouts to signal the region's agricultural prowess. On May Day, children danced around a maypole. It was easy to forget that Adolf Hitler's birthplace is only 90 minutes away and the Mau-thausen concentration camp much closer.

Now Fritzl has put Amstetten on the map of ghouls. He was born in the town just three years before the Nazis annexed Austria in 1938. Schoolfriends remember a boy so poor that other parents gave food to his mother. She lived by herself after divorcing Fritzl's father, a scandalous event in the small, traditional town. Nonetheless, he was said to have done well at school and was always well-behaved.

"Sepp" Fritzl was still a boy when Amstetten, strategically situated on a railway linking Vienna and the western city of Linz, sustained heavy allied bombing. His first brush with police came when he was 24 after a complaint that he had exposed himself. Police say he went on to rape at least two women in Linz, where he was working in the 1960s. Only one of the victims brought charges, resulting in an 18-month jail sentence; but another victim came forward last week saying that she recognised Fritzl from his photograph in the newspapers. A third woman from Linz also went to police last week to complain of an attempted rape by Fritzl. "He was a voyeur," one of the victims told police. "He used to ride around on his bicycle and watch everyone."

He got a job as an electrical engineer at a company that made industrial drills but decided in the 1980s to go into real estate and became, as Franz Polzer, the local police chief, put it, "a man of stature", a respected, well-connected figure in Amstetten, often seen at the wheel of a Mercedes, gold rings on his fingers, a gold chain round his neck. He was part of a well-heeled coterie of businessmen who were not short of friends in all the right places (though it is now known that he has debts of more than €2m - £1.56m - on his properties).

"For me, Sepp seemed an intelligent and successful man," said Leopold Styetz, a friend of Fritzl and vice mayor of Lasderg, a town not far from Amstetten. "He often talked about his family. He was very strict with his children, a strict but fair father, I would say. It was enough for him to snap his fingers and the youngsters would be in bed already. He always stressed that, for him, education and career were the most important things."

Not that Fritzl could not appreciate fun. Another friend, who went on holiday with him to Thailand, filmed him having a massage on a beach and cheerfully tucking into a knuckle of roast ham.

All the while, he was running a private concentration camp in his home. Even his holidays did not seem to interfere with that ghoulish routine. Somehow, he managed to keep the cellar supplied with enough air, energy and food to prevent his "underground" family from suffocating or starving to death. How had he managed to create this dual world?

With her fresh complexion and innocent smile - a fair ringer for Julie Andrews - Elisabeth was by all accounts Fritzl's prettiest daughter when she was young. She was not ostensibly his favourite, however. Friends remember the bullying paterfamilias hitting her for minor infringements of his disciplinary code.

According to police sources, he secretly began to abuse her sexually in 1977, when she was 11. The next year he applied for planning permission to extend his cellar into a nuclear shelter - with elaborate ventilation. With the support, no doubt, of his influential friends it was quickly granted. He also hugely extended the size of his house above the new bunker, building rooms that he let.

Liesel, as the girl was known, was "withdrawn" and undistinguished at school, a sign, according to child psychologists, of possible abuse. This was not picked up, however. Nor were her apparent cries for help followed up.

One of Fritzl's former tenants, Sepp Leitner, told Austrian television last week that a female neighbour had told him Elisabeth was being raped by Fritzl and that at the age of 16 she attempted to flee.

"She could not take it living at home any more and tried to escape," Leitner said. "She had taken sleeping pills and went to Vienna. But the police found her and they, or her father, brought her back home."

Leitner did not explain why he and the unnamed neighbour failed to alert the police about Elisabeth's plight, though he hinted darkly at their fear of the landlord's "revenge". He said he was still tormented by nightmares.

Fritzl waited until her 18th birthday to drug and drag her into the cellar, telling his wife and acquaintances that she had run away to join a cult. He assumed, arrogantly but accurately, that nobody would look too closely into his story.

"Nobody, apparently, showed any interest in the fate of this girl," said Hedwig Woelfl, the director of a child protection centre.

Fritzl told police last week he "meant well" in locking Elisabeth up, that he was acting in the girl's best interests to save her from drug addiction. In reality, he proceeded to rape his entombed daughter repeatedly over the following years, knowing that by now she was just another missing adult.

She has apparently told police that he initially kept her chained to the wall. For the first four years she was completely alone except when he appeared. Then she began to have her father's babies. He began to extend the cellar to accommodate his growing underground family, building a kitchen, bathroom and bedrooms.

Upstairs, meanwhile, life went on as normal. But after Elizabeth's first three babies had been born in the cellar he had a change of plan. For reasons that are still unexplained, the next time she gave birth, in 1993, Fritzl took the baby girl upstairs.

He told his wife that their errant daughter had left her on the doorstep of the house with a note asking them to look after her before running back to the cult.

The local authorities put up no objections to their adoption of the baby, whom they named Lisa after her mother. Social workers had no idea that Fritzl had a history of sex offending because, under the Austrian system, his rape conviction had been excised from his record after 10 years. "When such a crime has been atoned for, it's been atoned for," Polzer said last week.

Nor did the authorities react when two more babies - Monika and Alexander, both born in the cellar - were supposedly left on the doorstep by stealthy Elisabeth before dashing back to her sect. Fritzl and his wife were named foster parents, entitling them to state benefits.

"When Elisabeth's third child was laid at the door we asked Sepp if maybe he shouldn't try to find out about this sect," said Christina, 55, his sister-in-law, last week. "His answer was, 'no point'. His word was the law."

Christina is the one family member who stood up to the tyrant. She had hated him ever since his conviction for rape. "It was disgusting," she said, "particularly since he already had four children with my sister by that time."

She said Fritzl would often spend the night in the cellar, allegedly working on blueprints. "Rosie was not even allowed to bring him a cup of coffee," she said.

The family, meanwhile, lived in fear of his outbursts. "He was like an army drill instructor with his children. They had to stop whatever they were doing and stand still when he entered the room."

Christina also said Fritzl had gone to the expense of having a hair transplant after she told him that he was bald. "Josef would be spiteful about my weight, but I would say, 'better to be chubby than bald'. He is so vain that he went to Vienna for a hair transplant."

She claimed that Fritzl had not slept with his wife for years. "He would say, 'My wife is too fat for me'."

For Reinhard Haller, Austria's top criminal psychiatrist, it was not the desire for sex that pushed Fritzl, however. "It was a drive for power," Haller said. "He's probably a person with one very weak spot which he compensates for through sadism. He wants to have 100% control over his victims. That is his kick. The absolute power of the patriarch. He probably would have carried on doing this until he no longer had the power to control his hostages if nothing had gone wrong."

As the years went by, Fritzl would have his way with his daughter in a padded room while their children watched television, the one luxury he allowed them. Sometimes, in a grotesque semblance of a happy family, Elisabeth and the children would watch the television with Fritzl, who enjoyed motor racing.

It is reported that she never told her children that they were all imprisoned but did her best to create an illusion of normality. She would try to relieve the boredom by making models with the children out of cardboard and glue. She read them adventure stories "about princesses and pirates", police said.

What did the children make of this meagre experience of the outside world? The television images beamed into their dungeon might as well have come from another planet.

Frank Furedi, professor of sociology at Kent University, said yesterday: "The meaning of anything is specific to our circumstances . . . the mother would have known what a television was before she entered the cellar. She would have gone into the cellar understanding a TV to be a means of communication and entertainment - she may have even known that it was something used by mothers as a kind of digital babysitter. For the children, the television would have been very much an artefact, an empty map which they could fill in according to their imagination.

"If your whole life is spent in a cellar, and you've never been outside nor had any contact with other people, then the idea of there being a difference between your reality and an outside reality would be very difficult to conceptualise. There is no point of comparison and therefore even if you saw people standing outside houses on TV it would be something that you would not understand."

Fritzl's double life began to unravel last month when Kerstin, the eldest of the cellar children, became seriously ill and lost consciousness. Elisabeth convinced her father that unless he took Kerstin to a hospital, she would die.

On April 19, Fritzl drove Kerstin to Amstetten-Mauer clinic where doctors discovered a note that Elisabeth had slipped into her pocket. Fritzl told doctors that she had been left in front of his doorstep and described how his daughter had gone off to join a cult, occasionally sending them children to look after.

"Please help her," the note said. "Kerstin is afraid of people. She has never been in a hospital before. Please ask my father to help. He is the only person that she knows."

Doctors were not sure what to make of Kerstin's illness and launched an appeal for information on the whereabouts of her mother. Elisabeth saw the appeal on television on April 26. She persuaded Fritzl to take her to the hospital.

He led her and the two other children upstairs, announcing to his wife that Elisabeth had suddenly returned with her new children.

He then took Elisabeth to visit Kerstin. An anonymous caller tipped off police that Kerstin's mother was about to arrive at the hospital. Elisabeth was arrested: she was wanted for having left babies on her father's doorstep.

At first she stuck to her father's story about joining a cult. She then began to talk, offering a full account of her ordeal after receiving assurances that she would never have to set eyes on her father again.

Fritzl's long masquerade was over. He was arrested, and police started to unravel the dreadful story as counsellors rushed in. They witnessed remarkable scenes as the two boys who had lived in the cellar discovered fresh air, sunshine and normality for the first time.

"Is God up there?" little Felix asked, when he first saw the moon after being rescued. And when he saw the sun he was even more excited, making a squeaking noise.

Berthold Kepplinger, head of the clinic looking after the family, said that they were "devouring" the coverage of their release on television and in newspapers.

In one of the strangest family reunions in history, the "upstairs" and "downstairs" families were brought together one evening last week in the sanatorium.

Stunted and pale after spending the whole of their life without ever feeling wind or rain on their faces, Stefan and Felix were introduced to their more privileged siblings from above ground. The latter have been described as "well adjusted", each of them playing an instrument in the school band.

The most dramatic moment, by all accounts, was when Rosemarie took her long-lost, prematurely white-haired - and now toothless - daughter in her arms and apologised, saying: "I had no idea."

Some experts were baffled by the fact that this 68-year-old member of the local parent-teacher association had not yet been questioned by police as a potential suspect in the presence of her lawyer. By the end of last week it was being reported that she had received packages at the Fritzl home addressed to Elisa-beth.

Polzer, the policeman in charge of the Fritzl investigation, has raised eyebrows by describing as "unfair" the idea of considering Rosemarie as a suspect. His description of Fritzl as a man of "extraordinary sexual potency" also seemed somewhat misplaced.

As shock and shame gripped Austria, neighbours and former tenants began talking about what they had seen going on in the building. One witness told the cameras he had seen Rosemarie helping Fritzl to unload groceries from a wheelbarrow into the cellar. But why had nobody come forward when the horror was unfolding right under their noses?

Josef Haslinger, a novelist, thinks Austria's habit of sweeping unpleasant bits of history under the carpet may have something to do with Amstetten's blindness to Fritzl's subterranean world.

"There is this pretty, shiny surface that Austrians like to show, but it hides a monstrosity," he said. "On the surface we have moral standards and enlightened policies, but in the background we have this perverse world that nobody wants to talk about. We are still not able to accept our mistakes. So forgetting has become part of the mentality. If you look too closely you might have to act. So nobody looks."

The theme dominates much Austrian art, particularly novels by Elfriede Jelinek, who has been accused of executing "hysterical" portraits of Austrian perversity. Tales from the Vienna Woods, a play by Odon Von Horvath that debuted in Berlin in 1938, also high-lighted the syndrome.

"The Austrian character has a hidden, dark side," said Haslinger. "If we talk about it so much in our art, there must be something there in reality."

Haslinger was not alone in pointing his finger at a national malaise. Kampusch, who was a freckle-faced 10-year-old when she was kidnapped on her way to school in 1998, said she thinks Austria's past complicity with the Nazis is at least partly to blame.

Abuse exists worldwide, she said, "but I think it's also a ramification of the second world war". During the Nazi era, "the suppression of women was propagated, an authori-tarian education was very important", added the 19-year-old, whose dramatic escape from her own dungeon of despair in August 2006 captured global attention.

She was suggesting that Fritzl, who told his daughter that she would be "gassed" if she tried to escape from the bunker, belonged to a generation that thought it could get away with anything.

Some asked why nobody had ever challenged Fritzl's authority. "Female submission and obedience is an occurrence that is not being sufficiently questioned in our society," said Leo Prothmann, a psychothera-pist and analyst. "Why is the argument that this man was a patriarchal head of a family with 'high intelligence' being accepted as an explana-tion?

"The sad truth is that a patriarchal figure is seen as normal in our society and it is also being presented as such. That is why the wife did not know anything specific about the income of her husband. That is why she did not suspect him. That is why she accepted what the police called an investigation into a missing person as adequate.

"That is why she cared for the new children without asking any questions."

Hans Rauscher, a respected columnist, called for better social services rather than campaigns to salvage Austria's image.

"The Amstetten case is related to the climate of obedience to authority and lack of civic courage that is often seen in Austria," he said. "Fritzl was an authoritative coercer and neither the neighbours nor the authorities have questioned his facade of respectability."

Austria seems destined for a period of bleak introspection. "Of course it is right to look for answers," was how Josef Friedrich, an Amstetten musician, put it last week. "And the answers are slumbering deep within ourselves."