Josef Fritzl today claimed that he had been abused as a child at the start of his trial for imprisoning his daughter in the cellar as a sex slave for 24 years.

The 73-year-old retired electrical engineer admitted rape, incest and false imprisonment, but denied enslaving Elisabeth in the soundproofed basement of his home as the rest of his family remained oblivious upstairs.

He also denied murdering one of the seven children he fathered with Elisabeth in the cellar.

“I had a very difficult childhood,” Mr Fritzl said in a trembling voice at his trial in St Pölten, Austria.

“My mother didn’t want me. She was 42 when she had me. She simply didn’t want a child and she treated me correspondingly. I was beaten.”

Earlier Mr Fritzl held a blue lever-arch file in front of his face, hiding his features in defiance or shame, as he shuffled into the courtroom escorted by police.

He told the three judges and eight jurors that, at the age of 12, he had made it clear to his own mother that he would not tolerate being beaten any longer and would defend himself.

“From that point on, I was Satan personified for her,” he said. She never showed him any affection and his father appeared only “rarely and sporadically”, he said.

His relationship with his mother was never close, even though they shared the same house until her death in 1980.

Mr Fritzl attributed his mother’s coldness to her own childhood. “Her life wasn’t the best, either,” he said. “She grew up on a farm and had to work from the age of eight.”

Mr Fritzl is accused of imprisoning his daughter in the windowless cellar where no natural light penetrated, raping her on average three times a week, fathering seven children by her and allowing one of them to die by failing to seek medical treatment when it suffered breathing difficulties at three days old.

Outlining the case against him, Christiane Burkheiser alleged that he did not speak a single word to 18-year-old Elisabeth for the first few years of her captivity in the basement.

The chief prosecutor claimed that as time went on he raped her repeatedly in full view of the children and that he once punished her by shutting off electricity to the dungeon.

“[The defendant] showed no sign of regret or any consciousness of wrongdoing,” she said.

“Josef Fritzl treated his daughter as his property, he made her completely dependent. He decided what kind of food was brought into the dungeon. He decided when food was brought. And food was also often scarce.”

Ms Burkheiser made a mark on the entrance door to the court room at exactly 1m 74cm to illustrate the height of the ceiling at the highest point of the dungeon and pointed to it with a laser pointer.

“They had to crawl on their knees in order to get around the dungeon,” she told the court.

“It was damp and mouldy. The dampness crept into their backs and into their bones.”

She went towards the eight jurors with a box of musty objects and scraps of cloth, from the cellar. “Smell these things,” she urged the jury, who flinched back in their seats.

Ms Burkheiser, who is 32 and conducting her first major case since being made chief prosecutor, said that he had treated his daughter as a toy – an allegation linked to the enslavement charge, which Mr Fritzl denies.

She is pressing for life imprisonment in an institution for the criminally insane.

Rudolf Mayer, defending, appealed to the jury to be objective and not swayed by emotions. He insisted Mr Fritzl was “not a monster” and said his client even brought a Christmas tree down to his captives.

“If you just want to have sex, you don’t have children,” Mr Mayer said. “As a monster, I’d kill all of them downstairs.”

Before the hearing he described his client as nervous. “He told me, ’I’m scared, Mr Mayer,”’ he said.

Prompted by the judge several times, Mr Fritzl today pleaded “partially” guilty to rape. Austrian law differentiates between the severity of rapes and levels of coercion, and takes into account the degree of violence used and the consequences for the victim.

Mr Fritzl’s lawyer will clarify which part of the rape charges he rejects during the closed-door part of the trial this week, said Franz Cutka, a court spokesman. In theory, Mr Fritzl could plead guilty to the rape charge in general but dispute the prosecution’s claims as to the degree of violence he used.

None of Mr Fritzl’s alleged victims was present in court for the opening of the trial. They will remain in the sanctuary of a psychiatric clinic this week to escape the publicity surrounding the trial.

The trial ranks as one of the most extraordinary in modern Austrian history, overshadowing even the case of Natasha Kampusch, the schoolgirl who was held for more than eight years in an underground dungeon in a dormitory suburb of Vienna.

Mr Fritzl refused to lower the file which he was holding in front of his face until the television cameras, which were allowed into court for the first ten minutes of proceedings, were expelled by Judge Andrea Humer, 48. Only then did he lay the file on the desk in front of him and stare impassively ahead.

Amid extraordinary scenes he also declined to speak as the 95 journalists allowed into court for the start of the hearing shouted questions and thrust microphones towards him.

Tomorrow, on the second day of the trial, an eight-member jury will hear taped evidence from Elisabeth detailing her ordeal. The 11 hours of evidence was recorded last July so she would not have to see her father in court.

A verdict is expected by Friday.