Josef Fritzl arrives in court for the second day of his trial

The daughter and three of her seven children fathered by Mr Fritzl were kept captive in the cellar until the case came to light in April last year, when one of the children became seriously ill and was taken to hospital.

Mr Fritzl is accused of murdering one of the newborn twin boys his daughter gave birth to in 1996, having failed to arrange medical care for the ailing infant.

Some legal experts have said it may be hard to prove the murder charge but the charge of enslavement carries a maximum penalty of 20 years, and some of the other charges carry a sentence of up to 15 years.

'Normal behaviour'

Court spokesman Franz Cutka said the first day's proceedings had included "an interrogation of the accused", and the video recording by Mr Fritzl's daughter, about which he was then questioned.

FRITZL CHARGES AND PLEAS Murder - not guilty plea Enslavement - not guilty plea Deprivation of liberty - guilty plea Rape - partially guilty plea* Incest - guilty plea Coercion - guilty plea *Understood to mean he is contesting the wording of the charges In pictures: Josef Fritzl trial Timeline: Austrian cellar case Profile: Josef Fritzl

But he stressed that due to the sensitivity of the trial, no details of the proceedings could be released.

In her opening statement, prosecutor Christiane Burkheiser said Mr Fritzl had shown "no sign of regret or any consciousness of wrongdoing".

She alleged that he had not spoken to his daughter for the first years of her captivity, descending to the cellar only to rape her before returning upstairs.

Mr Fritzl, said the prosecutor, treated his daughter like his own property, sometimes raping her in front of their children in the cellar.

The defendant himself, his voice almost inaudible, talked to the judge about his childhood, saying he had been beaten by his mother.

Asked if he had any friends, he simply replied "No".