A 73-year-old Austrian man who held his daughter in a cellar for 24 years and fathered seven children by her is due in court.Questions are now being raised over whether anyone knew about Elisabeth Fritzl's captivity after Josef Fritzl, an electrical engineer, confessed to the crimes in what Austrian media have branded "The House Of Horrors".Elisabeth, now aged 42, says her father lured her into the cellar in 1984 and drugged and handcuffed her before imprisoning her.Police said a letter apparently written by her surfaced a month after her disappearance, asking her parents not to search for her.Elisabeth and three of the children lived in the 60-square metre (645 sq ft) cellar in Fritzl's nondescript two-storey home, which officials said was no more than 1.7 metres (5 ft 6 in) high and contained a padded cell.Media commentators want to know how 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.Fritzl, whom police described as "dynamic, bossy and authoritarian", had hidden the entrance behind shelves, and only he knew the code for the concrete door.Investigators have been combing through the cells where the victims were held captive, removing boxes of evidence from the building, which is home to several other families.Franz Polzer, head of criminal investigations for the state of Lower Austria, said Fritzl had made a number of confessions including the admission that he "forced himself physically" on his daughter.Commentator Petra Stuiber wrote in Austria's Der Standard newspaper that what she termed a rich self-satisfied society needed to examine why the crimes were allowed to occur."How is it possible that nobody heard or saw anything? How can it be that nobody asked questions?" said Ms Stuiber.Three of Elisabeth's 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.Fritzl had admitted to burning the body of one child in a furnace used to heat the building when it died soon after birth.Three other children - two girls and one boy - were adopted and brought up by Fritzl and his wife Rosemarie.Police have said they believe Rosemarie did not know what happened to her daughter when she disappeared in 1984. It was assumed Elisabeth had left voluntarily when her parents received a letter purportedly from the teenager saying they should not search for her.After Elisabeth disappeared, Fritzl said she had joined a sect and had left the children on the doorstep. He forced Elisabeth to handwrite letters to prove his claims, said the police.The case was exposed when Elisabeth's 19-year-old daughter 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.Fritzl faces up to 15 years in prison if charged, tried and convicted on rape charges, the most grave of his alleged offences under Austrian law, officials said.