St Poelten, Austria / Berlin  - "He wanted to build up a second family in the cellar," Josef Fritzl's lawyer said Monday, as the trial opened of the 78-year old Austrian charged with imprisoning and raping his daughter for 24 years.

Fritzl - whose crimes shocked the world last year when the incestuous offspring locked in his windowless family cellar were discovered by police - pleaded guilty to seven counts of incest, and confessed to having falsely imprisoned his daughter Elisabeth, who was incarcerated for more than two decades in the makeshift basement cellar of his home.

Fritzl, whose arrest brought worldwide notoriety to the small Austrian town of Amstetten, admitted "partial" guilt for raping his daughter thousands of times. But that is where his defence lawyer drew the line.

The elderly Austrian - who hid his face behind a blue folder in front of TV cameras at the opening of the trial - denied the accusation of murder through negligence of one of the seven children he fathered in the windowless dungeon, protected by a concrete- reinforced steel door.

He also denied the charge of slavery, levelled by the state prosecutor for the conditions under which he held his daughter, "confined to 18 square metres" in the dark cellar for the first nine years of her captivity.

Before detailing 24 years of alleged abuse, prosecution lawyer Christiane Burkheiser told the jury to "forget everything you have read or heard to date about this case."

Burkheiser then proceeded to describe at length the circumstances which led her to accuse Fritzl of denying medical assistance to his daughter's newborn son, who died of respiratory problems which set in shortly after birth.

Fritzl's lawyer Rudolf Mayer retaliated during the first few hours of the five-day trial, criticising the media's branding of his client.

"Fritzl is no monster," he told the court Monday.

"If I only do this for the sex, I don't go making children, don't bring along school books and presents," Mayer said in defence of his client's actions.

"He wanted to build up a second family in the cellar," Fritzl's defence lawyer added.

Mayer denied the murder charge, saying that in the days following baby Michael's birth, Fritzl had "repeatedly gone into the cellar to check upon the child."

"That's not the behaviour of someone committing murder," Mayer said.

Elisabeth disappeared in 1984, and her father reported his daughter, then just 18, as missing. Shortly after he presented a letter in which she supposedly asked not to be found.

Four years later, Elisabeth's daughter Kerstin was born, and remained incarcerated in the cellar with her mother. Of the subsequent six children, two more remained below ground, where they were permanently deprived of daylight.

Three children, claimed to have been abandoned on the doorstep by a reclusive Elisabeth, were then raised in the family home upstairs by Fritzl and his wife.

One child, a twin, died shortly after birth.

For the prosecution, the murder charge holds the key to a life sentence. If convicted of slavery, Fritzl could face a maximum 20 years in jail, while rape carries a maximum
15-year sentence under Austrian law.

The case has been subject to sometimes ghoulish worldwide interest from the moment Fritzl was arrested in 2008, when he took Kerstin out of the dungeon and into hospital for medical treatment.

Doctors had appealed for relatives to come forward, and became suspicious when Fritzl brought Elisabeth to the hospital.

"This is the deed of an individual perpetrator, not the crime of a whole town, or an entire nation," Judge Andrea Humer cautioned the court at the start of the trial, aiming her message in part at the 200 journalists who had descended on St Poelten from around the world to cover the hearings.

Some elements of the media have been criticized for trying to take paparazzi photographs of the surviving but traumatised children as they recuperated at a residential clinic.

As Fritzl entered the courtroom, he kept his face hidden behind a document folder, and remained impassive to the questioning of an Austrian reporter. For five minutes he stood his ground, while a cameraman tried to catch a glimpse of his face.

It was only when he was stood facing the judges' panel from the witness stand, with his back to the public gallery, that he lowered the folder covering his face.

Two hours into proceedings, the judge excluded the media and public ahead of intimate details of the case being discussed. The privacy of the victims was paramount she said.

An 11-hour pre-recorded testimony by the only witness, 43-year-old Elisabeth Fritzl, is also being held back from public scrutiny.

The first part of the video statement was shown Monday, but the court's spokesman was not at liberty to speak about Fritzl's reaction to his daughter's taped testimony.

The jury - consisting of six men and six women - are also due to hear statements from four experts, including a neonatal report and a psychological assessment of Fritzl.

The jury are expected to reach a judgement Thursday or Friday, at which point its 12 members must deliberate with the three professional judges assigned to the case to determine the custodial sentence. (dpa)