AMSTETTEN, Austria (Reuters) - Austrian police sought answers on Tuesday on how a father managed to imprison a daughter in a windowless cellar for 24 years and have seven children by her without authorities and neighbors knowing.

Josef Fritzl, a 73-year-old electrical engineer, had confessed to holding his daughter captive in what Austrian media have branded “The House Of Horrors”, police said on Monday.

The daughter and three of the children lived in the 60 square meter (645 sq ft) cellar in Fritzl’s nondescript two-storey home that officials said was no more than 1.7 meters (5 ft 6 in) high and contained a padded cell.

A leading question was how what went on in the house, situated in a busy street with shops in the small industrial town of Amstetten, passed unnoticed for so long, particularly as Fritzl built extensions to the cellar.

Commentator Petra Stuiber wrote in Austria’s Der Standard newspaper that what she termed a rich self-satisfied society needed to examine why it was allowed to occur.

“How is it possible that nobody heard or saw anything? How can it be that nobody asked questions?” said Stuiber.

“This is an appalling crime. I know of no comparable case in Austria,” said Franz Prucher, head of security in Lower Austria.

Photographs of the house showed a narrow passageway leading into other rooms that included a cooking area, with children’s drawings on the walls, a sleeping area and a small bathroom with a shower.

Amstetten, situated in rolling hills about 130 km (80 miles) west of Vienna, has a population of about 22,000 people.

KAMPUSCH CASE

The case first emerged on Sunday and shocked Austria less than two years after an Austrian teenager, Natascha Kampusch, escaped after being seized as a child and locked up in a basement for eight years.

Elisabeth Fritzl, 42, says her father lured her into the cellar in 1984 and drugged and handcuffed her before imprisoning her.

Three of her children, aged 19, 18 and 5, had been locked up in the cellar with her since birth and had never seen sunlight. The younger two were boys, the eldest a girl.

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Three other children -- two girls and one boy -- were adopted and brought up by Fritzl and his wife Rosemarie.

Police said Fritzl had admitted to burning the body of a seventh child in a furnace used to heat the building when it died soon after birth.

Fritzl, whom police described as “dynamic, bossy and authoritarian”, had hidden the entrance to the cell behind shelves and only he knew the code for the concrete door.

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The case unfolded when the 19-year-old girl became seriously ill and was taken to hospital with severe cramp caused by lack of oxygen. Doctors appealed for her mother to come forward to give details of her medical history.

Fritzl brought Elisabeth and her remaining two children out of the cellar, telling his wife their “missing” daughter had chosen to return home, police said.

Elisabeth agreed to make a thorough statement to the police after receiving assurances she would have no further contact with her father, who she said abused her from the age of 11.

Police believe Josef’s wife did not know what happened to her daughter when she disappeared in 1984.

Fritzl had said Elisabeth had joined a sect and that she had left the children on the doorstep. He forced Elisabeth to handwrite letters to prove his claims, said the police.