Elisabeth helped her father Josef fix the door on his new cellar – then her world went dark

How it began

It had seemed an innocent enough request: could she help him hoist a door into its frame? Elisabeth Fritzl followed her father down into the bowels of the cellar that he had been building for months in the garden beneath the family home.

It was a hot day in August 1984, a month in which Prince released his hit Purple Rain, the space shuttle Discovery took off on its maiden voyage and the country of Upper Volta changed its name to Burkina Faso.

Elisabeth climbed down the stairs into the cellar and helped him fix the door in the dusty confines of his underground creation. As she turned to leave, a piece of cloth soaked in ether was held over her mouth and nose and her world went dark. Possibly forever.

It was a deeply cruel start to an unbelievably cruel deed. How could Elisabeth have known that she was helping her own father install the final building block to his plans to lock her up as his sex slave?

Fritzl had been planning what was effectively a dungeon for years, receiving official permission to construct his cellar complex as far back as the late 1970s.

It was not difficult to get officials to approve underground constructions. It was at the height of the cold war and this, after all, was Lower Austria, which during those tense and heady days in world affairs found itself on the frontier with the Soviet Union. Nuclear bunkers were seen as an even more normal and necessary addition to an Austrian home than a conservatory or a kitchen extension might be viewed in Britain.

The local council had even given him a grant of a couple of thousand pounds towards the building costs.

Neighbours had observed with some intrigue as the electrical engineer hired a digger, which sat in his garden at Ybbsstrasse 40 in the tidy town of Amstetten for months.

They watched as he tossed tons of earth from beneath the house and shifted it in a wheelbarrow to make way for the rooms he planned to build.

A precise planner, he had thought of every last detail, securing concrete and steel supplies through contacts at construction companies where he had previously worked. There were initially two access points – a heavy hinged door and a metal door reinforced with concrete operable via a remote-control device.

A total of eight doors had to be opened before reaching the purpose-built cellar. The final door before the darkness of the tomb-like cellar was the one that Elisabeth herself unwittingly helped him to install.

It was easy enough to instigate. Elisabeth had threatened to run away many times. More than once she had been hauled back to the family home by the police, or her father, once getting as far as the big city, Vienna, with a girlfriend. So when Elisabeth disappeared from one day to the next he told friends and family she had run off to join a sect. They all believed him.

In reality, she was living under their feet – beneath the garden where he and the rest of the family enjoyed barbecues in the summer. Years later, when he expanded the underground accommodation, he built a swimming pool upstairs, as a cover-up for the amount of earth he was having to drag up. Later when they splashed in the pool, the family did so above Elisabeth's prison.

Life underground

Over the next 24 years the horror for Elisabeth was unrelenting – the cold, the damp, the rats, which she was sometimes forced to catch with her bare hands, the water that ran off the walls in such large quantities she had to use towels to soak it up. Summer, when the place turned into an intolerable sweaty sauna, was the worst time of year, she would later write in a calendar.

During those years Mikhail Gorbachev called for perestroika and glasnost, Chernobyl's nuclear reactor blew up, DNA first came into use to convict criminals, the Berlin wall fell. There was Tiananmen Square. The release of Nelson Mandela. The LA riots after the beating of Rodney King. OJ Simpson was arrested for murder. Rwanda. Diana, Princess of Wales died. The euro was introduced. Mad cow disease. Slobodan Milosevic went on trial. A tsunami devastated Asia. Not to mention all the inventions and technological developments – from the mobile phone to the internet.

For everyone else, the world kept on spinning, while Elisabeth's stood still and stagnant.

At first Fritzl strapped up her arms and then tied them behind her back with an iron chain, which he then secured to metal posts behind her bed. She could only move approximately half a metre either side of the bed.

After two days he gave her more freedom of movement by attaching the chain around her waist. Then, about six to nine months into her imprisonment, he removed the metal chain because "it was hindering his sexual activity with his daughter", according to the indictment.

He sexually abused and raped her sometimes several times a day, from the second day of her incarceration right up until her release in April 2008.

Over the course of nearly a quarter of a century he would rape her at least 3,000 times, resulting in seven babies who themselves often had to watch the abuse as they grew older. Three of these children were to stay underground, never seeing daylight until their release in April last year.

Three others mysteriously appeared on the doorstep of Fritzl and his wife, Rosemarie, in their home in Amstetten, west of Vienna – abandoned, so Fritzl told the community, by Elisabeth, who had delivered them to him and Rosemarie from her sect, to be brought up as the Fritzls' own. And all without arousing Rosemarie's suspicions or those of the Austrian authorities.

A 'devoted father'

Fritzl dictated letters to her which she wrote from her prison, driving sometimes miles in his car to post them back to his wife Rosemarie. In them, Elisabeth explained that she was well, but could not look after the children.

In reality, she was torn at being separated from her children but happy that her "upstairs" offspring would at least have a better life than those languishing downstairs.

One of the children, a twin called Michael, died shortly after his birth in the cellar in 1996. He had severe breathing difficulties and expired in his mother's arms when he was just 66 hours old.

Fritzl admitted he subsequently burned the baby's body in an incinerator, but – until his admission during his trial this week – always denied that he was responsible for murder through negligence. "I don't know why I didn't help," he told the court. "I just overlooked it. I thought the little one would survive."

Until Wednesday, Fritzl had also denied enslavement. His lawyer, Rudolf Mayer, tried to explain Fritzl's decision to imprison his daughter and force her to submit to his every whim as the act of a devoted father.

Fritzl's original defence for how it all began was that Elisabeth was a wayward child, and that he was only trying to protect her by locking her away from the outside world. Drugs, drink and bad company had threatened to drag her down, he argued.

His lawyer tried to paint him as a caring man, who spent time and money maintaining both of his families - he even took a Christmas tree down into the dungeon, said Mayer. And school books. An aquarium. Even a canary. In what now seems like a sick joke he said that the canary's ability to survive was proof that the air in the cellar could not have been that bad after all.

Throughout her captivity he repeatedly threatened Elisabeth by saying: "If you do not do as I say, your treatment will get worse and you will not escape from the cellar anyway."

He repeatedly beat and kicked her. He also subjected her to humiliating sexual abuse, including forcing her to re-enact scenes from violent pornographic films. The abuse left her with serious lasting physical injuries and psychological damage.

She spent the first five years entirely alone. He hardly ever spoke to her.

Babies were company

Then the babies started to come. They were a horror for her. But they also provided her with longed-for company, and a purpose to live after years in which she had contemplated suicide.

The births – over 12 years – all took place without any medical help. To prepare for them, her father provided her with disinfectant, a dirty pair of scissors and a 1960s book on childbirth.

Fritzl often threatened Elisabeth and her children, warning them that if they tried to escape they would be killed. The indictment said: "He told them he had installed a system so that the doors would give them electric shocks if they tried to open them and that poison would be released into the cellar if they tried to escape, killing them all instantly."

He would punish her by switching off all the power to the cellar for days at a time "so she was left alone in total darkness".

She cried as the freezer he later installed so that he could stockpile food while he went away on holiday defrosted and leaked its contents on to the floor of her already horrendously damp prison.

A way out

The end of her ordeal came last April when Kerstin, her 19-year-old daughter, became gravely ill. Fritzl, not known for his mercy in the past, put her in his Mercedes and drove her to hospital.

There, the doctors became deeply suspicious of the deadly pale creature with bad teeth who lay dying in intensive care.

Repeated media appeals were broadcast for the mother to come forward with information that was necessary if they were going to have any chance of saving her life.

Elisabeth and her two boys viewed the appeals on the television in their cellar. She pleaded with her father to let her out. His powers waning, his ability to keep two families sustained reducing by the day as he aged and his heart grew weaker, he had already begun to hatch a plan as to how he could release his daughter without too many questions being asked. He relented perhaps for the first time ever. He told the hospital the family had appeared on his doorstep, having escaped from their sect.

But the doctors and police did not believe his story this time round. At the hospital Elisabeth was whisked into a room away from her father, where police threatened to charge her with child abuse because of the way she had clearly neglected her daughter.

Elisabeth said she had a completely different tale from the one they expected to hear. She would start to tell them only on condition they promised her she would never have to set eyes on her father again.

· This article was amended on Friday March 20 2009. Rodney King was beaten but not murdered, as we said. This has been corrected.