Kate Connolly, one of only two British journalists in the court in St Pölten, witnesses the opening of the case against Josef Fritzl

Josef Fritzl, the Austrian electrical engineer on trial for incarcerating his daughter in an underground prison for 24 years and fathering seven children with her, yesterday pleaded guilty to charges of rape, incest, false imprisonment and coercion.

The 73-year-old denied one charge of murder for the death of a twin boy born to his daughter, for whom Fritzl failed to seek medical help. He also denied a charge of slavery, which has been on the Austrian statute book since the 1960s, but has never been tried in court. Fritzl faces a minimum sentence of 15 years in prison, and a maximum of life.

Prosecutor Christiane Burkheiser told the court how Fritzl had raped his daughter an estimated 3,000 times while holding her in appalling conditions.

She said he had lured his daughter into the purpose-built cellar in August 1984 when she was just 18, on the pretence of asking her to help him fix a door. He then sedated her by placing a cloth soaked with ether over her nose and mouth and slammed the door closed.

On the second day after her incarceration, he put an iron chain around her stomach, attaching it to a pole "so that she had no chance of escape".

He raped her the same day for the first time, Burkheiser said.

She said the underground cell had been "his playground" and that he had "used [Elisabeth] like a toy".

"He came, took her and went again," she said.

Listing the dates Elisabeth had given birth over a 12-year period, Burkheiser spoke of the pain she had felt at her father's decision to take three of the children to live with him upstairs.

"Can you imagine what that was like for her, on the one hand the relief that the child would have a better life, on the other, the fact that he was taking away her dearest?" she asked.

She detailed how his failure to fetch medical help for a twin boy called Michael, born to his daughter in 1996, had led to his death, and how he later disposed of the body by burning it.

Defending Fritzl, Rudolf Mayer said his client was not a monster, as he had been portrayed by the media. "Despite the way he's been described, try to see the accused as a human being," he told the eight-strong jury and four replacement jurors. He argued that Fritzl could have let the cellar children die and that his determination to provide for both his "upstairs" and "downstairs" families was proof that he was not a monster.

Having submitted his pleas on the six charges, Fritzl then answered detailed questions from Humer about his childhood, early adulthood and career, including his apprenticeship as an electrical engineer.

Fritzl said he had hardly known his father, who had only played a "periodic and sporadic" role in his life, and that had been abused as a child by his mother. "I had a very difficult childhood," he said in a weak and sometimes barely audible voice. "My mother rejected me. She was 42 when she had me. She just didn't want a child and she treated me accordingly."

He said he had been hit repeatedly, even for bringing school friends home. "I had friends but mother didn't allow them.

I got a clip round the ear every time. Then when I was 12 I said to her: 'If you do that again I'll hit you back,' and then she stopped."

Asked if he had any friends in adulthood, Fritzl said: "I had no friends. You need to nurture friendships and I had no time for that."

He told the court that he had met his wife, Rosemarie, at the age of 19, and she had been "the first woman I had sexual relations with". She had been "very domesticated, and wanted at least 10 children".

The press and public were made to leave the courtroom before a video of Elisabeth Fritzl was played on a huge screen. Investigators recorded an interview with her last July in the presence of psychiatrists, to spare her the ordeal of having to face her father in person.

Court officials said the 11-hour long recording will be played to the court in "small portions" throughout the week, due to their apparently harrowing content.

Four expert witnesses are also on hand to give evidence. For the duration of the trial, Elisabeth and her six children are being looked after in the nearby psychiatric clinic they were taken to after their release last year, having been allegedly hounded out of their new home by British paparazzi.

One British tabloid has published pictures of Elisabeth in her new environment, while another has printed the name of the village where the family had set up home in a new house.