Meanwhile, forensic investigators have been continuing to search the 60 square metre cellar beneath Fritzl's two-storey home in Amstetten.
"Down there it is just chaos at the moment. We have to go over every detail very carefully," Franz Prucher, head of security in Lower Austria said.
Forensics experts removed boxes of belongings from the cell underneath Fritzl's apartment in the working-class town 120km west of the capital Vienna.
Drugged and handcuffed
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 in the cellar with her since birth and had never seen sunlight.
The younger two were boys, the eldest a girl.
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 when the baby died soon after birth.
Prosecutors said on Tuesday that they are looking into the possibility of charging Fritzl with "murder through failure to act'' in connection with the baby's death.
Fritzl would face up to 20 years in prison if tried and convicted on such a charge.
Franz Polzer, head of the lower Austrian bureau of criminal affairs, said he did not blame authorities for missing the case.
"I have not been made aware of any error on their part. Fritzl was a very cunning man. He not only fooled his wife, but officials, the police, everyone," he said.
|"Fritzl was a very cunning man. He not only fooled his wife, but officials, |
the police, everyone"
head of the lower Austrian bureau of criminal affairs
Police said that they have checked Fritzl's property holdings as a precaution and that he had not maintained any other secret prisons.
However, Polzer would neither confirm nor deny Austrian media reports that Fritzl had had past run-ins with the law.
"If there was an offence outside of the statute of limitations, I can't comment on this," he said.
Guenther Moerwald, head of St Poelten prison, said Fritzel was calm when he arrived at the prison on Monday and had been put in a cell where he can be monitored in case he tries to commit suicide.
Mental health experts said Fritzl was likely to have suffered from a "power complex" and other psychiatric disorders.
Reinhard Haller, an Austrian psychiatrist, said Fritzl appeared to have been driven by pronounced narcissism and a need to exercise power over others and that that may have helped explain how he got away with the abuse for so long.
"This man must have been insane and must have felt he was far superior to others," Haller said.