But the police found her and she was sent back to her father, Josef Fritzl.

More abuse followed, and when she turned 18, she was locked up by him in the labyrinth of cells under the family home, not to emerge again till now, a broken 42-year-old woman who bore seven children as a result of years of incestuous rape.

As police investigations into the House of Horror in Amstetten continued, more details of the Fritzl family emerged at the weekend.

Mr Sepp Leitner, a former lodger in Fritzl's house for four years in the 1990s, told Austrian media that a neighbour had told him that her friend, Elisabeth, had been raped by her father.

According to Mr Leitner, a waiter, the neighbour even helped young Elisabeth to run away to Vienna but the teenager was tracked down by police.

He did not explain why he and the unnamed neighbour failed to alert the police to Elisabeth's plight, though he hinted at their fear of the landlord's 'revenge', the Times of London reported.

Mr Leitner, who stayed for four years in a ground-floor flat above the cellar, believes he may have unwittingly paid for the utility costs for the underground prison.

He recalled that he had had disputes with Fritzl over his electricity bill, which soared to more than £300 (S$800) in one quarter. Even when all his electricity was turned off, the meter continued to run.

'If only I had tried to get to the bottom of it, instead of letting it go, maybe the dungeon would have been discovered much earlier. I'm now angry at myself that I failed to do that,' he said.

Mr Leitner also recalled that food often went missing from his kitchen and that of fellow tenants, and how Fritzl would 'unload plastic bags full of shopping from his silver grey Mercedes and bring them into the garden between 10 and 11 at night'.

Elisabeth, who was living just metres away underground, was first abused by her father when she was 11, in 1977. The following year, Fritzl successfully sought building permission to extend his cellar and make a bunker that could resist nuclear fallout, the Times reported.

It was unclear at this stage if he was already making plans to imprison his daughter, the only one of his children who refused to be cowed.

After her brief escape to Vienna, there was another brief interlude at age 16 when she left home to work as a waitress and lived in a hostel.

Two years later, she was drugged and handcuffed and kept underground by her father, who went on to put out the story that she had run off again, this time to join a Satanic sect.

When she gave birth, he claimed she had dumped the babies on his doorstep. 'When Elisabeth's third child was laid at the door, we asked him if maybe he shouldn't try to find out about this sect,' says Mrs Christine R, sister of Fritzl's wife, Rosemarie. 'His answer was: 'No point'. His word was law.'

Meanwhile, the Austrian authorities are said to have uncovered documents that indicated Fritzl, 73, had two previous convictions: an attempted rape of a 21-year-old woman in a forest near the city of Linz in 1967, and sexual assault on a 24-year-old woman in Linz a month later.

Depending on the crime, a conviction in Austria can be expunged after five but no longer than 15 years, unless the crime carries a life sentence. That meant that when Fritzl reported his daughter missing 24 years ago and routine background checks were carried out, there was no trace of his previous convictions.

Casual acquaintances describe Fritzl as a hard worker and jovial fellow who liked a bawdy joke. But there were hints of a troubled childhood, the Independent reported.

His sister-in-law said he was brought up by a single mother with an explosive temper. 'Josef grew up without a father. His mother raised him with her fists,' Mrs R said.