On 19 April 2008, Fritzl agreed to seek medical attention after Kerstin, Elisabeth’s eldest daughter, fell unconscious. Elisabeth helped him carry Kerstin out of the chamber and saw the outside world for the first time in 24 years. He forced her to return to the chamber, where she remained for a final week. Kerstin was taken by ambulance to a local hospital, the Landesklinikum Amstetten, and was admitted in serious condition with life-threatening kidney failure. Fritzl later arrived at the hospital claiming to have found a note written by Kerstin’s mother. He discussed Kerstin’s condition and the note with a doctor, Albert Reiter.
Medical staff found aspects of Fritzl’s story puzzling and alerted the police on 21 April. The police broadcast an appeal on public media for the missing mother to come forward and provide information about Kerstin’s medical history. The police reopened the case file on Elisabeth’s disappearance. 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. The police contacted Manfred Wohlfahrt, a church officer and expert on cults, who raised doubts about the existence of the group Fritzl described. He noted that Elisabeth’s letters seemed dictated and oddly written.
Elisabeth pleaded with Fritzl to be taken to the hospital. On 26 April, he released her from the cellar along with her sons Stefan and Felix, bringing them upstairs. He and Elisabeth went to the hospital where Kerstin was being treated on 26 April 2008. Following a tip-off from Dr. Reiter that Fritzl and Elisabeth were at the hospital, the police detained them on the hospital grounds and took them to a police station for questioning.
Elisabeth did not provide police with more details until they promised her that she would never have to see her father again. Over the next two hours, she told the story of her 24 years in captivity. 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. Shortly after midnight, police officers completed the investigation. Fritzl, aged 73, was arrested on 26 April on suspicion of serious crimes against family members.
During the night of 27 April, Elisabeth, her children and her mother Rosemarie were taken into care. Police said Fritzl told investigators how to enter the basement chamber through a small hidden door, opened by a secret keyless entry code. Rosemarie had been unaware of what had been happening to Elisabeth.