An elderly Austrian confessed Monday to imprisoning his daughter in a windowless cellar for 24 years and fathering her seven children, prosecutors said.
Josef Fritzl, 73, "admitted building the dungeon and to holding his daughter and three children there," prosecution spokesman Gerhard Sedlacek told AFP.
Fritzl admitted incest "but insisted there was no force involved," said Sedlacek.
One of the children died shortly after birth. "He disposed of it in the furnace of his building," chief investigator Franz Polzer told a press conference in the eastern town of Amstetten, about 100 kilometers (60 miles) west of Vienna, where the family lived.
Fritzl was to be brought before an investigating magistrate on Monday and faces several more days of questioning over the case which has shocked Austria.
His daughter Elisabeth, now 42, has alleged she was drugged by her father in August 1984 and had been his prisoner ever since, giving birth to seven children in the "dungeon".
The six surviving children are three boys and three girls aged between five and 19.
The case came to light after the eldest of the six children, Kerstin, was admitted to hospital on April 19 with serious health problems. Doctors looking for background information stepped up efforts to find the mother and the whole horrific story came to light when Fritzl allowed them to establish contact with his daughter.
Elisabeth Fritzl and three of her children, who had until now never seen sunlight, were kept in three cramped underground rooms in the family house.
Photographs of the rooms, measuring "50-60 square metres in all," with a ceiling just 1.70 metres (5.5 feet) high, according to Sedlacek, were released by police. They showed a well-furnished living area, with sink, shower, a small kitchen area and two small bedrooms.
The cellar was hidden behind a reinforced concrete door which could only be opened with a numbered code. There were no windows and the prisoners' only contact with the outside world were a radio, television and VCR.
This ironically helped Elisabeth Fritzl escape, after she saw the hospital's appeal on television for more background information on Kerstin and persuaded her father to let her out, Polzer said.
Kerstin was "critical but stable," doctors at the hospital where she was being treated, said, without giving more details.
Franz Pucher from the Lower Austrian police told journalists: "This case is unique in this country's criminal history."
Polzer said however there was "a wide range of questions that still need answering" such as how Fritzl supplied the woman and children with food, how the babies were born and cared for in such cramped conditions, and how he could have incarcerated his victims for so long without his wife knowing.
Fritzl legally adopted three of the children -- two boys and one girl -- when they were still babies. He is said to have told his his wife Rosemarie, 69, -- with whom he had seven children -- and local authorities that his daughter had left the babies on the doorstep.
Each delivery was accompanied by a letter purportedly signed by her saying she could not support the child because she already had others to care for.
Elisabeth Fritzl also told investigators her mother knew nothing about the sexual abuse she had endured since the age of 11, some seven years before she was locked away.
The trio went to school as normal, seemingly unaware that their mother and three other siblings were trapped underground.
Neither neighbours nor social services appear to have had any inkling, either.
It is the latest in a series of horror abuse cases to have stunned Austrians, with the Oesterreich tabloid calling it "the worst crime of all time," and the Kronen-Zeitung portraying Fritzl as a "monster, a brutal tyrant."
DNA tests are being carried out to confirm if he is the father of the six surviving children.
Austria's most notable sequestration case was that of Natascha Kampusch, who was kidnapped on her way to school in 1998, and held captive for over eight years in the basement of a house near Vienna before escaping two years ago.
Three young girls near Linz, in northern Austria, were also locked up for seven years by their mentally ill mother.