On 29 August 1984, her father lured her into the basement of the family home under the pretense that he needed help with carrying a door,

Josef Fritzl was born on April 9, 1935 in Amstetten, Austria. In 1956, at the age of 21, he married Rosemarie, 17, with whom he had seven children: two sons and five daughters including Elisabeth, who was born in 1966. He is suspected of having begun abusing Elisabeth in 1977 when she was 11 years old.

After completing compulsory education at age 15, Elisabeth started a training course to become a waitress. In January 1983, she ran away from home and, together with a friend from work, went into hiding in Vienna. She was found by police within three weeks and returned to her parents. She rejoined her training course and, upon completion in summer 1984, was offered a job in the nearby city of Linz.
Years of captivity
On 29 August 1984, her father lured her into the basement of the family home under the pretense that he needed help with carrying a door. He drugged her with ether and moved her into a small concealed underground chamber. Unknown to anyone else, he was to keep her imprisoned until her release on 26 April 2008.
After Elisabeth's disappearance, her mother filed a missing person report. Almost a month later, her father handed over a letter to the police, the first of several that Elisabeth would be forced to write while in captivity. The letter was postmarked in the town of Braunau. It stated that she was staying with a friend and was tired of living with her family, warning her parents not to look for her or she would leave the country. Her father stated to police that she had most likely joined a religious sect.
Over the course of the following 24 years, Fritzl visited her in the hidden cellar on average once every three days to bring food and other supplies. After his arrest, he admitted that he repeatedly had sexual intercourse with his own daughter and had done so against her will.
Elisabeth gave birth to seven children during her years in captivity. One child died shortly after birth, and three children — Lisa, Monika and Alexander — were removed from the cellar as infants to live with Fritzl and his wife. They adopted Lisa and became Monika's and Alexander's foster carers, with the knowledge of local social services authorities. Officials said that Fritzl "very plausibly" explained how three of his infant grandchildren had appeared on his doorstep. The family received regular visits from social workers, who did not hear complaints or notice anything to arouse their suspicions.
Following the birth of the fourth child in 1994, Fritzl enlarged the prison for Elisabeth and her children from 35 m² (380 sq ft) to 55 m² (600 sq ft). The captives had a television, radio, and video cassette player at their disposal. Food could be stored in a refrigerator and cooked or heated on hot plates., Fritzl shut off the lights to the basement or refused to deliver food for several days at a time.
Fritzl told Elisabeth and the three children (Kerstin, Stefan and Felix) who remained in the cellar that they would be gassed if they tried to escape; investigators have concluded that the threat was empty and was primarily designed to frighten the captives as no actual gas pipes were found leading into the basement.] Fritzl stated after his arrest that it was sufficient to tell them not to meddle with the cellar door or otherwise they would receive an electrical shock and die.
According to his sister-in-law Christine, Fritzl would go into the basement every morning at 9 a.m., apparently to draw plans for machines, which he sold to firms. Often he stayed down there for the night — his wife was not even allowed to bring him coffee. A tenant, who rented a ground floor room in the Fritzl house for 12 years, said he heard noises coming from the basement but Fritzl passed it off as noise emanating from the gas heating system.