'Herr Fritzl, can you just answer one thing – why?'

Trial begins with shocking account of crimes that appalled the world

Josef Fritzl may have been described as the "face of evil" but all that was visible yesterday was a single "evil" eye. It peered through a metal ring in the back of a bright blue folder that masked the face of the world's most infamous rapist as he stepped unsteadily across the floor of an Austrian courtroom flanked by burly police guards.

As his trial on charges of multiple rape, murder, incest, coercion and slavery opened in the Lower Austrian capital of Sankt Pölten, Fritzl did his best to hide. Wearing a houndstooth check jacket, grey shirt and diagonally striped tie, the 73-year-old former engineer trembled as he held the folder pressed to his face for what seemed like a small eternity

As is the custom in Austria, a reporter from state television was allowed to fire questions at the accused before he took his seat in the dock. In a bizarre piece of courtroom theatre the journalist repeatedly asked him: "Herr Fritzl can you just answer one thing – why?" But for nearly 10 minutes, Fritzl just stood there shaking behind his folder and said nothing.

When cameramen were ordered to leave the courtroom, the accused sat down in the dock with his back to the public and jurors. They were afforded a view of the unkempt crop of grizzled grey hair on the back of his head and his legs, nervously twitching as the charges were read out against him. Only the judges could see his face.

Fritzl has been called the "Incest Monster". It is not difficult to understand why. After his arrest in his home town of Amstetten almost a year ago, the sickening details of his crimes, which were rapidly made public, were almost unbearable to read. Yesterday the details of his offences, stripped of all media hype, were even more shocking for being read out in court.

Josef Fritzl is accused of kidnapping his daughter Elisabeth when she was 18 and imprisoning her for the next 24 years in a windowless cellar beneath his home. He is accused of raping her, an estimated 3,000 times, and fathering seven children through his incestuous relationship with her. All of the children were born underground and without medical assistance. One of the children, a baby boy, became ill and died. Fritzl is alleged to have incinerated his corpse in a central heating furnace to destroy the evidence.

Three of the children were sent upstairs as babies to be looked after by Fritzl's wife Rosemarie. However the other three children and their mother spent their whole lives underground until their release last April.

Yesterday, slumped on his courtroom seat in front of judges and eight jurors, Fritzl pleaded guilty to charges of multiple incest and imprisonment, but insisted that he was only "partially guilty" of rape and coercion and entered pleas of not guilty to charges of slavery and murder in connection with the death of his son.

As she read out the charges against Fritzl, the Austrian state prosecutor Christiane Burkheiser gave a chilling resumé of his crimes. She said there were two versions of the truth. "There was the man who cared for his family as a respectable member of the community and then there was the real truth about the man who took his daughter into a cellar, tied her up and secured her by a leash round the waist", she said. He then subjected her to multiple rapes, according to the charges.

Mrs Burkheiser used a blue laser pointer to impress on the jury the fact that the ceiling of Fritzl's cellar was only five feet from the ground. "He kept his daughter in a room that measured only 11sq m for nine years. That is just about the size of the jury box you are sitting in," she said.

Describing his daughter Elisabeth's suffering as an " unimaginable martyrdom", Mrs Burkheiser said that Fritzl's cellar had no heating, no shower and no warm water and hardly any ventilation for the first nine years of her imprisonment. "In the summer it was blisteringly hot. In the winter it was freezing cold. Nobody can really imagine what went on down there," she said.

The state prosecutor, who had personally inspected the cellar, added; "There is a morbid atmosphere down there. You have to crawl on your knees to get in. The door is only 83cm high. It is damp, mouldy and smelly. The dampness creeps into your back and into your bones. Fritzl raped his daughter down there on the second day of her imprisonment," she said. The jurors were asked to gain an impression of the stinking atmosphere in the cellar by smelling a number of objects taken from the prison and passed round in a box.

Mrs Burkheiser said that, during the first few years of her imprisonment, Frtizl did not speak to his daughter at all but just descended at random and raped her. "He would turn down the lights, rape her and then turn the lights back up," she said. After the children were born, Fritzl raped her repeatedly in front of them. Elisabeth was kept in the cellar in complete darkness and without electricity for periods of up to 10 days.

"He was the absolute ruler," said Mrs Burkheiser. "He decided what should be eaten and what medicines were taken down. But the worst thing of all was not the raping and the appalling conditions. The worst thing was the uncertainty. She never knew when he would come, when he would go or when he would come back. It is the uncertainty that breaks a person."

The prosecutor at one point turned to the defendant and asked him directly: "Mr Fritzl, how could you treat your own flesh and blood like that?" Fritzl appeared to flinch when asked the question, but he refused to answer.

Frtizl was said to have provided Elisabeth with a dirty mattress, a filthy blanket and a rudimentary book about childbirth only a few weeks before she was due to give birth.

In 1996, after the birth of her son Michael, Fritzl knew that he was suffering from breathing difficulties, but did nothing, Mrs Burkheiser said. Two days later the baby died. Mrs Burkheiser said that Fritzl's failure to act made him guilty of murder.

Fritzl had told his daughter that he had installed three locking doors and electronically operated light barriers which would flood the cellar with gas if Elisabeth tried to escape. "She would never have tried. She was a broken woman," said Mrs Burkheiser.

In his defence Fritzl spoke about the "troubled childhood" he experienced when he was young and of how he spent periods in foster homes. "My mother did not allow me to have any friends," he said. "But I had one secret friend and he let me down. After that I never wanted to have any more friends."

His lawyer, Rudolf Mayer, said he had been subjected to death threats in the run-up to the trial. He insisted that his client was not "a monster" and asked jurors to be persuaded by the facts rather than emotions.

The court was later shown clips of the main evidence against Fritzl – an 11-hour videoed interview with his daughter in which she tells the story of her imprisonment. All her evidence is being held in camera. A verdict is expected on Friday.

Legal experts said Fritzl would face life imprisonment if convicted of murder but as little as 15 years if convicted of some of the other offences. Psychiatrists have recommended he spend the rest of his life in a secure institution. However state prosecutors said if Fritzl could demonstrate that he had made a recovery he could be freed after serving half of a 15-year term.

Elisabeth Fritzl and her children were moved back to the hospital where they recovered from their ordeal for the duration of the trial. The Austrian authorities have given them new identities and enforced a no-fly zone over their current accommodation during the trial to deter journalists.