Elisabeth Fritzl and her children could have been freed years earlier if Austrian authorities had not missed dozens of clues, writes Stefanie Marsh, author of a new book on the man who held his daughter in a dungeon for a quarter of a century.
There is a theory, popular in Austria, that Josef Fritzl was a cunning and extremely stealthy criminal. But, having spent the past year researching the case, I have found that the opposite is true.
Josef Fritzl apparently left a number of clues that were ignored by officials
He is ruthless, and an accomplished liar, but he is also a clumsy operator, a man who, by the time he had reached his mid-40s, had been arrested twice for arson, twice more for sex offences, and jailed once for the rape of a woman at knifepoint.
And though the Austrian authorities have always insisted that they bear no responsibility for Josef Fritzl's 24-year incarceration of his daughter, Elisabeth, evidence I have seen suggests that this often flagrant criminal left a staggering number of clues in his wake - clues that were repeatedly ignored by social workers, the police and the judiciary.
In August 1984, four months after her 18th birthday, Elisabeth disappeared. She vanished at some point around lunch-time. She was living at the family home in Amstetten at the time and, except for her father, the house was empty. Her mother and one of her sisters were out shopping, another sister had been sent out by Fritzl for a walk.
By the time they returned, Elisabeth was gone. It was Josef Fritzl who, the next day, would report Elisabeth's disappearance to the police, hinting, without a shred of evidence to back up his claim, that she had joined "a cult".
Notwithstanding the fact that there are no cults to speak of in Austria, either now or at the time, there were other factors that might have alerted the police's suspicions.
Although Fritzl's conviction for rape had by this stage been wiped from his criminal record (by Austrian law sex offences were then automatically deleted from police files after a period of 10 to 15 years), it was commonly known in the tight-knit community that he was a convicted rapist. His arrests for arson were still on record but he nevertheless legally owned two guns: a Bernadelli pistol and a rifle.
The alleged abuses took place at this house in Amstetten
It was also known to social workers that Elisabeth had run away from home two years previously. On her return to Amstetten, however, they had chosen to discuss the matter only with her father, though Elisabeth was in the room at the time.
Additionally, some of her friends suspected Elisabeth of self-harming - another obvious outward sign of abuse - but social workers simply accepted Josef Fritzl's account.
We now know what in fact happened on that August afternoon in 1984. Josef Fritzl had locked his daughter into a specially prepared dungeon in his cellar. About a month into her incarceration, he forced her to write a letter which he then posted to himself and showed the police.
Again the authorities accepted everything Fritzl told them at face value. The letter was never examined by a relevant expert, despite the fact that Austria's expert on fringe religions actually lived in Amstetten (he would eventually be shown all Elisabeth's letters only in 2008, declaring them obvious fakes).
In 1993, nine years after Elisabeth disappeared, the first of three babies appeared on the Fritzls' doorstep. The precise details of these "discoveries" are particularly disturbing.
The first child was abandoned in a cardboard box along with a letter from Elisabeth. However, in a nonsensical piece of bureaucratic logic it was decided that there would be no official search for Elisabeth because she was an adult and could "go where she liked."
Fritzl forced his daughter to write letters from the dungeon
Just over a year later there was a second child, this time found abandoned on the doorstep in a pram. It was Rosemarie Fritzl who discovered this second child and it was she who then described what had happened to a social worker.
She said shortly before midnight she had heard the sound of a baby crying outside the house. She discovered the child on the doorstep and returned inside with it in her arms. Suddenly the telephone began to ring. On the other end of the line a woman, claiming to be Elisabeth, was apologising for having abandoned her child. It was obviously a taped message. Rosemarie Fritzl hung up, but the phone immediately began to ring again. When she picked up the same message was played down the receiver.
What was particularly mysterious to Mrs Fritzl, she told the social worker, was the fact that she and her husband had recently changed their home telephone number and this number was not yet known to anyone else.
Although the case of the two foundlings was unusual enough to attract the attention of the national press, nothing about this chain of events seems to have caused much concern among the authorities.
At Josef Fritzl's suggestion, one of the letters was examined by a graphologist who, of course, declared himself to be satisfied that it had indeed been written by Elisabeth Fritzl.
The fact that her letters never made any mention of a cult, and that, in later years, at least one letter would bear a postmark from a town very close to Amstetten, in which Josef Fritzl was known to own a house, still did nothing to alert social workers or the police. A third child would appear on the Fritzls' doorstep in 1997. He, too, would be taken in and raised by his "grandparents".
Time passed. Josef Fritzl spent more and more time in the cellar but nobody questioned his increasingly unusual behaviour. He was living apart from his wife, in a separate flat within the house in Amstetten, and he would often spend the night in the cellar, claiming he was away on a business trips.
Lodgers saw him bring bags of groceries into the cellar, as well as building material, appliances, and furniture: bed frames, mattresses, a shower unit, a washing machine. Things were constantly disappearing into the cellar and never coming out.
In late March 2008, Elisabeth Fritzl's oldest child, Kerstin, became desperately ill in the cellar and her father decided to evacuate her. Had it not been for the suspicions of one of the doctors treating Kerstin in hospital, it is more than likely the case would never have come to light.
The Austrians have prided themselves on their discreet handling of the case, but there has been no inquiry, no admission of failure on behalf of the police, social workers, or the government.
The Austrian media, for their part, have been side-tracked into a largely peripheral debate about press intrusion.
And, although it is true that the British paparazzi in particular resorted to desperate and underhand tactics to get the first pictures of Elisabeth Fritzl and her children, many sections of the Austrian press showed no compunction in either publishing Josef Fritzl's confidential psychiatric report before his case came to trial, or printing many of the intimate details of Elisabeth Fritzl's ordeal when they were first leaked to an Austrian magazine.
So much for privacy.
Meanwhile, serious questions regarding the competence, gullibility and accountability of the Austrian authorities have gone unanswered.
Stefanie Marsh is a senior features writer at The Times. The Crimes of Josef Fritzl: Uncovering The Truth by Stefanie Marsh and Bojan Pancevski is published this month by HarperCollins.