The giveaway sign was probably the missing blue ringbinder. It was Josef Fritzl's nod to the Austrian court and to the world that he had capitulated, that his realm of power and domination had collapsed.

As he shuffled into court today without the most potent symbol of this trial, which out of shame and embarrassment he had held up to cover his face during previous sessions, he made a decision that elicited gasps from the public gallery.

"I recognise that I am guilty of all the charges presented," he said. "I regret what I've done."

Asked by the stunned judge, Andrea Humer, what had made him change his mind so suddenly, and prompted him to admit to the charges of murder and slavery that he had previously rejected, Fritzl said: "Because of the video testimony of my daughter."

On a large television screen the previous day, Elisabeth, 42, had confronted her father with the full horror of her 24-year ordeal in hour after hour of harrowing prerecorded testimony. She detailed everything, from the years of violent sexual abuse, often in front of her children, to how he tortured her in the dark, damp and cold cellar, and let her repeatedly give birth without medical help, allowing one of her children to die.

A point in that testimony which reportedly left a searing impression on the court was her remark: "I screamed many times during all those years, but nobody ever heard me."

Fritzl told the court in a strained and croaky voice: "I should have realised it before, but I only realised yesterday for the first time how cruel I was to Elisabeth."

"You mean," the judge asked him, "you recognised for the first time what she had experienced just as she depicted it?" - to which Fritzl nodded.

Reports were rife today that Elisabeth had slipped into court on Tuesday to watch the man who stole her life squirm as he heard her damning testimony.

The respectable Kurier newspaper reported that she had been brought to the court under cover of darkness from the nearby clinic where she and her family are living for the duration of the trial. A member of staff from the clinic told the newspaper: "She's planning to write a book and simply wanted to gather her impressions." In the evening, amid tight security, she was taken back to the clinic and her six children, all of whom were born in the cellar, the source said.

Her testimony had a "devastating effect" on Fritzl, according to his lawyer, Rudolf Mayer. He said the full force of it hit Fritzl when he returned to his prison cell that evening and requested to see a counsellor.

Mayer would neither confirm nor deny whether Elisabeth had been present at the court. But he told the Guardian: "If Elisabeth was indeed in the court then I'm of the opinion that it would have been the trigger for his devastation.

"He asked to see a psychiatrist afterwards, so crushed was he. The testimony which he saw for the first time had a profoundly devastating effect on him and led to the change of direction in this trial."

Mayer's client had not informed him in advance of his decision to plead guilty, he said. "I was indeed surprised, not least because someone with such a personality disorder as he has - which involves keeping up appearances and giving the impression that he's the one with the power - finds it difficult to drop his trousers in front of the world."

Fritzl's decision to confess to the murder through third-party negligence of his son Michael, born to Elisabeth in 1996, who died of severe respiratory problems after 66 hours of life, brought to a close to one of the most controversial aspects of the trial. Asked by Humer why he had not taken the sick child out of the dungeon and sought medical help, Fritzl whispered: "I don't know why I didn't help. I just overlooked it. I thought the little one would survive. I should have recognised that the baby was doing poorly."

Earlier in the week, state prosecutor Christiane Burkheiser had told the court how Elisabeth had given birth to Michael and his twin Alexander without any medical assistance, as she had all her children, and using just a pair of unsterilised scissors, a dirty blanket, a 1960s manual on childbirth and a bottle of disinfectant.

She also presented the jury with a box of objects from the cellar which were still contaminated with the rancid, damp smell that Elisabeth had lived with for 24 years, urging them: "Smell, smell those 24 years."

As he was escorted into court today flanked by 11 guards, the sallow-skinned Fritzl cut the figure not of a tyrant, but of a broken man, his hands shaking, his back curved and his shoulders stooped under the same black and grey small-check jacket he was wearing when he was arrested in his home town of Amstetten in April 2008.

He listened passively, his hands crossed on his lap, alternatively sitting with his legs crossed or nervously jigging his left leg and wiping his nose with a tissue, as psychiatrist Adelheid Kastner told the court that his mother's failure to love him as a child was central to understanding Fritzl's subsequent behaviour and his need to dominate and possess a person for himself.

"Herr Fritzl spent most of his childhood in a state of anxiety," Kastner said. She added that the more children Elisabeth had given birth to in the cellar, "the more power he felt he had over her".

Reports by technical experts read out in court went some way to explain how Fritzl operated his underground empire. They concluded that a timer switch, which he claimed would open the door after a set period in case he died or fell ill, did not in fact exist.

Until today's confession, Fritzl had stubbornly refused to admit that he had caused Elisabeth much suffering, arguing instead that he had saved her from a life of ruin and debauchery when he lured her into the cellar at the age of 18, at a time - he falsely claimed - when she was living a life dominated by drink and drugs. He told authorities she had joined a sect, and that over the years had dumped three of her children on his doorstep, unable to cope. It was a story that they failed to question for more than two decades.

Fritzl's defence lawyer had insisted to the court earlier this week that his client was not a "monster" as he has been portrayed in much of the media. Mayer argued that Fritzl had struggled to look after both his family upstairs - wife Rosemarie and three of Elisabeth's children, whom he had brought up from the cellar to live with them upstairs - as well as his "underground" family. He brought them food, school books, a television, and even a Christmas tree, Mayer said. He said if he had only wanted to keep his daughter as his sex slave, he would not have had children with her. But if the jury felt any sympathy whatsoever towards the man whom the prosecutor said gave many the impression that he was the "nice old man from next door", it was then hit by the full impact of Elisabeth's evidence, which laid bare the horror of her life. Counsellors were on hand, as well as four replacement jurors ready to step in if the evidence proved too hard to stomach.

Fritzl will face a sentence of between 20 years and life imprisonment. But it is possible that his confession will lead to a reduced sentence. "It all depends on whether the jury and the judges take the confession to be a mitigating circumstance," said the vice-president of the court, Franz Cutka.

The court's judges retired at around midday to formulate a series of questions for the jury, which will be put to them this morning. The jury will then retire to decide their verdict based on both the evidence and Fritzl's confession, and to determine the sentence.

The court is expected to hear their decision this afternoon. Authorities will then decide over the next two weeks where Fritzl will be sent.

It is likely that he will be transferred from his prison cell in St Pölten to a psychiatric institute following Kastner's recommendation yesterday that he needed to undergo intensive therapy to treat a serious personality disorder, and that untreated, he was capable of carrying out further crimes even at his advanced age.

Fritzl is on suicide watch, meaning at the end of each day's court sessions guards remove his tie and belt to ensure he cannot use them to harm himself.