A jury ordered Josef Fritzl detained for life yesterday for imprisoning his daughter as a sex slave in his cellar during a 24-year orgy of depravity in which he fathered seven children.

The court in the Austrian town of Sankt Poelten said Mr Fritzl would have to spend the rest of his life interned in a mental institution after a psychiatrist warned that the married 73-year-old felt "born to rape".

If, at a later stage, doctors found Mr Fritzl cured, he would have to serve the rest of his sentence behind prison bars.

The jury found him unanimously guilty of murdering one of the seven children through negligence, as well as all other charges of rape, incest and sequestration in the basement of the family house in Amstetten.

Mr Fritzl at first denied murder and enslavement but changed his plea after being confronted by the video testimony of his daughter Elisabeth whom he raped on thousands of occasions, sometimes staying downstairs overnight.

As the sentence was handed down, a composed Mr Fritzl merely said: "I accept the verdict".

Mr Fritzl's lawyer, Rudolf Mayer, said his client found the verdict "fair".

"After confessing to 3,000 instances of rapes, 24 years of captivity in a cellar plus murder, it's obvious that such a sentence will be handed down," Dr Mayer told journalists. "Obviously, he thinks this sentence is fair."

Before the verdict had been announced, Mr Fritzl had made a last expression of remorse.

"I'm sorry from the bottom of my heart," the 73-year-old retired engineer told the eight jurors before they retired to quickly reach their unanimous guilty verdict.

"Unfortunately, I can't change anything now."

But chief prosecutor Christiane Burkheiser said the remorse shown by Mr Fritzl was a sham.

"Don't believe him, he's shown his true face in trying to exploit people's gullibility," she said of Mr Fritzl and his stunning change of heart on Wednesday when he pleaded guilty to enslaving Elisabeth as well as murder.

The murder charge related to the death of a new-born twin boy called Michael whom Mr Fritzl did nothing to help when aware that he was mortally ill.

Elisabeth Fritzl, now 42, went to the court on Tuesday to see her father's reaction to 11 hours of video testimony she recorded for the trial.

Elisabeth's lawyer Eva Plaz also poured scorn on Mr Fritzl's show of remorse, saying the woman wanted her father "to be held accountable until he dies".

"Don't believe one word from the defendant. The defendant wanted to be master over life and death," she said.

Mr Fritzl had admitted the other four charges against him - incest, rape, sequestration and grievous assault - but pleaded not guilty to murder and slavery when the trial opened on Monday. Psychiatrist Adelheid Kastner told the court on Wednesday that Mr Fritzl posed a danger and should be held in a mental facility. Mr Fritzl was emotionally stunted, the psychiatrist told the court.

"He is aware - he says so himself - that he has an evil side. He is aware that he was born to rape. He has that partly under control. But as soon as he loosens his grip, everything erupts out."

Mr Fritzl, who ruled his family with an iron fist, locked his daughter up in a cellar of his home on August 29, 1984. He said she had joined an obscure sect.

Three of the surviving children were brought to live with Mr Fritzl and his wife Rosemarie, 69, while the other three spent their entire lives in the dungeon, never seeing daylight.

The case broke last April after the eldest child, a 19-year-old girl named Kerstin, fell severely ill and Elisabeth begged her father to bring her to hospital.

DNA tests later confirmed Josef Fritzl was the father of Elisabeth's six surviving children, aged five to 19.

The jury was told how Elisabeth had initially had to live without hot water, heating, fresh air or sunlight in a narrow cellar. Mr Fritzl gradually expanded the dungeon to 40 square metres.

Elisabeth and her family are now at a secret location while the authorities attempt to help them build a new life.