Watching the gruesome details of the Austrian incest case unfold, one question is on many people's minds: "How could this be allowed to happen?"

The plight of Elisabeth Fritzl, who was held by her own father for 24 years in a windowless prison and bore him seven children, has set a new standard for criminal depravity in postwar Austria following the case of Natascha Kampusch, who escaped in 2006 after being held for eight years in a basement.

While the Kampusch case was widely regarded as the exceptional crime of a twisted loner, Austrians are now faced with a case even more unfathomable within less than two years.

Hours after the case came to light in the town of Amstetten, officials, police and even the victims' lawyer lined up to say that no one but the suspect could possibly be at fault; Josef Fritzl, now 73, had simply outsmarted them all.

In his first public reaction, Chancellor Alfred Gusenbauer expressed great concern for the victims and quickly announced a campaign to repair Austria's image abroad.

Much to the surprise of international media and anger of welfare charities, there seems to be little effort to investigate the circumstances that might have allowed the crime to go unnoticed by neighbours and authorities alike.

"The story of Elisabeth F. shows that unanswered questions and neglected inquiries made it possible for the father to continue his abuse," said Hedwig Woelfl, head of research at the Austrian child protection charity Moewe. "The aid network failed in terms of bringing the information together."

Elisabeth's disappearance should have been a clear sign that something was wrong, but apparently nobody was interested in the teenage girl, and the family, the town, the authorities and the country itself did not ask enough questions, she said.

Many of the questions focus on how Mr Fritzl could have been allowed to adopt one and foster another two of the children from his incestuous relationship. Mr Fritzl had been granted the adoption after pretending the child had been left on his doorstep by his missing daughter with a handwritten letter asking her parents to raise the child.

Judge Josef Schloegl, who in 1994 approved the adoption of the now 15-year-old girl, said that at the time, he had not asked for Mr Fritzl's police record.

"We had no reason to ask for it," Judge Schloegl said.

"I have three reports from the juvenile welfare office that the family is very lovingly caring for the little child, and that everything is fine... It was the perfect case file."

Austrian media have reported that Mr Fritzl had two previous convictions. Since non-capital offences are purged from criminal records in Austria after a maximum of 15 years, they could have lapsed before the adoption.

At a news conference, local official Hans-Heinz Lenze said authorities had asked for Mr Fritzl's police record at the time, but found no offences against his name.

Even more of a puzzle is how Mr Fritzl managed to build the 60 square- metre basement prison, including sanitation facilities, a refrigerator, freezer and washing machine, without attracting attention. And how could his wife Rosemarie and all those who lived in the house over the past 24 years not have noticed anything?

Franz Polzer, head of the criminal investigation unit in the province of Lower Austria, urged those who had lived at some point in the unremarkable two-storey block owned by Mr Fritzl to come forward.

"Over the past 24 years about 100 people have lived in this house of horrors - some for a short time, some for longer... Perhaps any one of them may have seen something noteworthy that at the time may have seemed insignificant."

But it seems to many, that Austrian officials might have some way to go before they are ready to have a close look at where the system might have failed Elisabeth.

Asked if anyone else could be at fault, officials at the news conference fell into gloomy silence before Franz Prucher, head of security in Lower Austria, repeated a well-known line.

"We cannot say at the moment whether someone will have to take responsibility. At the moment I see no omission by anyone," Mr Prucher said.