Mr Fritzl claims he wanted to control his daughter's behaviour
Josef Fritzl, the Austrian man accused of imprisoning his daughter in a cellar for 24 years, acted without an accomplice, Austrian officials say.
Prosecutor Gerhard Sedlacek told the Austrian press agency that he believed Mr Fritzl, 73, acted alone.
Police say Mr Fritzl raped his daughter Elisabeth and fathered seven children with her.
Forensic experts are still examining the windowless cellar dungeon where he kept her and several of her children.
Former lodgers at the Fritzl house in Amstetten, Lower Austria, had raised the possibility that other people may have been aware of the existence of the purpose-built dungeon, a claim investigators said was unlikely.
Mr Fritzl has been in custody since his arrest at the end of April. He has not yet been formally charged.
Franz Cutka, vice president of the court in St Poelten, where Mr Fritzl is being held, said it was still unclear when a trial would be held and that it was likely to be closed to the public, with only limited media access.
Mr Fritzl's alleged crimes came to light when Elisabeth's eldest daughter Kerstin became seriously ill in April.
She was allowed out of the cellar and admitted to hospital in Amstetten.
Police then issued an appeal to Elisabeth Fritzl to contact them about her daughter, and later picked up Mr Fritzl and Elisabeth near the hospital.
Mr Fritzl has said he was driven by an addiction that "got out of control".
Elisabeth and her children are continuing to be cared for at a psychiatric clinic. Their lawyer, Christoph Herbst, has said they are likely to be given new identities and that they may also consider relocating to another country.