DNA tests showed that Austrian Josef Fritzl, who raped his daughter and kept her prisoner in a windowless cellar for 24 years, was the father of her six surviving children, police said on Tuesday.
Fritzl has confessed to imprisoning his daughter Elisabeth in the cellar beneath their two-storey home and fathering seven children by her.
Prosecutors said they were investigating Fritzl over the death of the seventh child and that he could face a charge of killing the child through neglect.
"The resultshows that the six children, which the unfortunate Elisabeth Fritzl gave birth to in the basement, have all been undoubtedly fathered by her own father, the now 73-year-old Josef Fritzl," Franz Polzer, head of the criminal investigation unit in Lower Austria, told a news conference.
Police have said Fritzl has admitted to burning the body of the seventh child when it died soon after birth.
"Josef F. is being investigated for murder by failing to render assistance," local chief public prosecutor Peter Ficenc told Reuters.
Investigations were also being conducted for rape, incest and coercion, Ficenc said.
Investigators were still searching the 60 square metre (645 sq ft) cellar beneath electrical engineer Fritzl's home, Franz Prucher, head of security in Lower Austria said.
"Down there it is just chaos at the moment. We have to go over every detail very carefully," Prucher told Reuters.
Fritzl appeared before a judge in St Poelten, the provincial capital of Lower Austria, on Tuesday, who ordered that police could keep him in detention while inquiries continue.
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Officials said Fritzl said nothing on the advice of his lawyer. He was calm when he arrived on Monday and had been put in a cell where he can be monitored in case he tries to commit suicide, said Guenther Moerwald, head of St Poelten prison.
Elisabeth Fritzl, 42, says her father lured her into the cellar of their home in 1984 and drugged and handcuffed her before imprisoning her.
Three of her children, aged 19, 18 and 5, had been locked in the cellar with her since birth and had never seen sunlight. The younger two were boys, the eldest a girl.
