Fritzl had assaulted, sexually abused and raped his daughter countless times during her imprisonment inside a concealed area in the cellar of the family home.

[14] According to an annual report for 1967 and a press release of the same year, he was also named as a suspect in a case of attempted rape of a 21-year-old woman and was known for indecent exposure.

As a result, more than 25 years later, the local social service authorities did not discover his criminal history when he applied to adopt and/or foster Elisabeth's children.

[20] On 22 November 1986, two scuba divers found Posch's body wrapped in two olive green tarpaulins on the southern shore of Lake Mondsee.

[22] After his arrest, Fritzl was investigated for possible involvement, since at the time of the murder, he and his wife ran a campground which was located opposite where Posch was found.

[23][18] In addition to Posch's murder, Fritzl was looked into as a suspect in the death of Anna Neumayer, aged 17, who was killed with a captive bolt pistol in a field in Linz on 17 August 1966.

In extracts from talks with his lawyer, Fritzl said that he "always knew during the whole 24 years that what I was doing was not right, that I must have been crazy to do such a thing, yet it became a normal occurrence to lead a second life in the basement of my house."

He suggested that the emphasis on discipline during the Nazi annexation of Austria, which ended when he was ten years old, might have influenced his views about decency and good behaviour.

The chief editors of News magazine noted in an editorial that they expected Fritzl's statement to form the basis of his lawyer's defence strategy.

He stood trial for the murder of the infant Michael, who died shortly after birth,[38] and faced between ten years' and life imprisonment.

[4] Over the next 24 years, Fritzl entered the hidden chamber almost every day, for a minimum of three times a week, bringing food and other supplies, and repeatedly raping Elisabeth.

Three—Lisa, Monika, and Alexander—were removed from the chamber as infants to live with Fritzl and his wife, who were approved by local social services authorities as their foster parents.

[11] Following the fourth child's birth in 1994, Fritzl allowed the enlargement of the chamber, from 35 to 55 m2 (380 to 590 sq ft), putting Elisabeth and her children to work digging out soil with their bare hands for years.

[28] According to his sister-in-law Christine, Fritzl entered the basement every morning at 09:00, ostensibly to draw plans for machines which he sold to manufacturing firms.

A tenant who rented a ground floor room in the house for twelve years claimed to hear noises from the basement, which Fritzl said were caused by the "faulty pipes" or the gas heating system.

Fritzl repeated his story about Elisabeth being in a cult, and presented what he claimed was the "most recent letter" from her, dated January 2008, posted from the town of Kematen.

Elisabeth recounted that Fritzl raped her and forced her to watch pornographic videos, which he made her re-enact with him in front of her children in order to humiliate her.

Fritzl told investigators how to enter the chamber through a small hidden door, opened by a secret keyless entry code.

[45] His defence lawyer, Rudolf Mayer, said that although the DNA test proved incest, evidence was still needed for the allegations of rape and enslavement.

[46] In their 1 May daily press conference, police stated that Fritzl had forced Elisabeth to write a letter the previous year, which indicated that he may have been planning to release her and the children.

Around 1981 or 1982, according to his statement,[28] Fritzl started to turn this hidden cellar into a prison chamber and installed a washbasin, toilet, bed, hot plate and refrigerator.

[56] Christiane Burkheiser, prosecuting her first case since being appointed Chief Prosecutor, pressed for life imprisonment in an institution for the criminally insane.

[68] In 2008, Austrian Chancellor Alfred Gusenbauer said he planned to launch a foreign public image campaign for his country, in light of the "abominable events.

After being taken into care, Elisabeth, all six of her surviving children and her mother were housed in a local clinic, where they were shielded from the outside environment and received medical and psychological treatment.

It has also been revealed that normal everyday occurrences, such as the dimming of lights or the closing of doors, plunged Kerstin and Stefan into anxiety and panic attacks.

[73] Lawyer Christoph Herbst, who represents Elisabeth and her family, said, "Fortunately, everything is going very well"; they spend their time answering hundreds of letters from all over the world.

The children, along with their mother, have made day trips, including swimming outings, where care was taken to keep them out of reach of the paparazzi and to protect their privacy.

Factors that traumatised the "upstairs" children include learning that Fritzl had lied to them about their mother abandoning them, the abuse they had received from him during their childhood, and finding out that their siblings had been imprisoned in the cellar.

[83] In March 2019, Mark Perry, a British journalist who interviewed Fritzl in his cell, said he showed no remorse for his crimes, recalling that he kept saying, "Just look into the cellars of other people, you might find other families and girls down there.

[85][86] In September 2021, a decision was made to release Fritzl from a psychiatric detention facility to a regular prison, where he was to continue to serve his life sentence.