But the 73-year-old pleaded innocent to a charge of enslaving his daughter Elisabeth for most of her life, according to Reuters news agency reporters at the closed-door trial.
The case, which sent a wave of revulsion through Austria and around the world, has draw hundreds of foreign journalists to the provincial court.
Fritzl, who arrived in court holding up a blue folder to prevent photographers from taking pictures of his face, remained silent and motionless, ignoring questions from television crews before the judge and eight-person jury entered and cameras were sent out.
They charged Fritzl with murder by neglect because he had failed to seek help for the baby, whose body he burnt in a furnace.
If he is found guilty of murder by the jury he could be given a life sentence or 10 to 15 years in prison.
His lawyer said Fritzl expects to spend the rest of his life behind bars.
Fritzl built a soundproofed cellar with a reinforced door under his home in the provincial town of Amstetten.
"He shut [Elisabeth] away in the cellar and made her totally dependent on him, forcing her into sexual acts and treating her as if she was his own property," his charge sheet read.
Fritzl's daughter and her six children, three of whom were incarcerated from birth, are now living in a secret location under new identities.
The case came to light when one of the three children who had never seen sunlight, 19-year-old Kerstin, fell seriously ill and was taken to hospital by Fritzl.
In comments via his lawyer last year, Fritzl said he had lived a "second life" in the cellar complex, watching adventure videos with the children and bringing flowers for Elisabeth, who cooked dinner.
Three of the children born in the cellar were raised above ground by Fritzl and his wife Rosemarie after he pretended Elisabeth had abandoned them.
Police say that Rosemarie did not know of her husband's actions.
The verdict is expected by the end of the week.