Josef Fritzl, the Austrian man who is accused of keeping his daughter captive in a cellar for 24 years, refuses to answer further questions, police say.
They said he had signed a statement admitting imprisoning and raping his daughter and fathering her seven children, but refuses to explain.
Franz Prucher, head of police in Lower Austria, said police would be investigating whether Mr Fritzl had committed any further crimes.
Mr Fritzl faces up to 15 years in prison if he is convicted of raping his daughter, among other offences.
Mr Fritzl has admitted to disposing of the body of the newborn in an incinerator shortly after the birth.
Elizabeth and three of the children were held captive in a windowless cellar under the family home.
She was allowed out of the cellar and admitted to hospital in Amstetten.
The other children who were not confined to the cellar lived an apparently normal life with Mr Fritzl as his “grandchildren” in the upper sections of the same house.
