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A photo taken by police Monday shows suspect Josef Fritzl at an unspecified location. Police allege he held his daughter captive for 24 years and fathered seven children with her. ((Police Niederoesterreich/Associated Press))

A 73-year-old Austrian man confessed Monday to imprisoning his daughter in a windowless cell in his basement for 24 years and fathering seven children with her, police said.

"He admitted that he locked his daughter, who was 18, in the cellar, repeatedly had sex with her and that he is the father of her seven children," said Franz Polzer, head of the criminal investigations unit in the province of Lower Austria.

Polzer said the man, Josef Fritzl, who was earlier identified only as Josef F., also confessed to tossing the body of a newborn baby boy into an incinerator when the infant died shortly after birth. 

"We are being confronted with an unfathomable crime," said Austrian Interior Minister Guentter Platter.

Hans-Heinz Lenze, a local official in the town of Amstetten, said the man's wife "apparently had no idea" of what was going on. She and the suspect had seven children of their own. 

Drugged, imprisoned in 1984

Three of the daughter's offspring were raised in the family home while the rest were kept hidden in the basement with their imprisoned mother.

"You have to imagine that this woman's world [just] fell apart," Lenze said.

Police said Sunday that a 42-year-old woman, identified as Elisabeth, told them her father lured her into the basement of the family home in 1984, and drugged and handcuffed her before imprisoning her.

Photos were released Monday showing the basement cell where the woman was held. It included a small bathroom and a narrow passageway leading to a tiny bedroom.

Investigators say an electronic lock with a keyless entry system and a soundproof door apparently kept the woman from escaping the cell, which was constructed of reinforced concrete.

Police picked up the woman and her father on Saturday at a hospital in a nearby town, where one of the surviving children was rushed unconscious with a serious, undisclosed illness.

3 children never went outside

In her statement, Elisabeth said her father began sexually abusing her when she was 11.

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An outside view of the house in Amstetten, Austria, where a 73-year-old man said he kept his daughter imprisoned, repeatedly raping her and fathering her seven children. ((Helmut Stamberg/Associated Press))

Her father allegedly locked her in a room in the cellar on Aug. 28, 1984. The woman was reported missing the next day and a month later, a letter surfaced, allegedly written by her, saying she didn't want to be found.

Police said the woman appeared "greatly disturbed" during questioning and agreed to talk only after authorities assured her that she would no longer have contact with her father, and that her children would be cared for.

The woman and her children are undergoing psychiatric care, officials say.

Three of the children were raised upstairs in the family house by Elisabeth's father and his wife. They went to school and lived relatively normal lives, according to police. The other three remained locked up in the cellar with their mother and none of them had been outside before last week.

Similar incident unearthed in 2006

Neighbours said Fritzl and his wife were quiet but friendly, and frequently shopped in local stores and talked to members of the community.

The CBC's David Common, reporting from Austria, said the story is causing shock and revulsion across the country.

"It's a very embarrassing day for Austria," Common said, "because this is the second time something like this has happened here."

Natascha Kampusch was 10 years old when she was kidnapped in 1998 on her way to school in Vienna. She was held by Wolfgang Priklopil for nearly nine years in a small dungeon in his home in the suburbs.

Hours after Kampusch escaped in August 2006, Priklopil killed himself by jumping in front of a train.

With files from the Associated Press