He was born to rape and poses a lifelong risk, doctor warns the court

Dr Adelheid Kastner warned that the 73-year-old had an untreatable sexual obsession and remained a threat to women for the rest of his life.

Dr Kastner, who gave evidence to the court for 40 minutes based on a 30-page report and hours spent with the rapist and killer, said Fritzl nurtured a fantasy of receiving a short prison term and rejoining his family in his old age. "He has a malicious vein, an almost unstoppable flood of destructive lava," said DrKastner. "He has a personality disturbance with narcissistic tendencies, emotional instability and emotional immaturity."

She added: "He feels torn apart. He wants to do everything positive, and then suddenly the evil side of him breaks out. Sometimes he is dominant with a sense of duty, and then at other times he forgets his duty and is irrational. For somebody who is born to rape he held out for a relatively long time.

"He couldn't sustain friendships and always made decisions by himself. The relationship to his daughter in the dungeon is probably the most reliable one in his whole life, proved by the fact that he completely misunderstood the dimension of his behaviour, and plainly assumed when his daughter made contact with the outside world she would do nothing to expose the events.

"During the entire period of his crimes he was aware of his responsibility and thus his criminal liability. It is to be feared in future he will again commit acts with serious consequences."

Dr Kastner said Fritzl's personality was formed out of a painful childhood. She detailed how his mother was a "violent woman" who had Fritzl "merely to prove to herself that she was fertile. Once he was born, he had fulfilled his function. There was no love, no care: he was a burden.

"He lived in an atmosphere that was dominated by fear. She hit him a lot. It was absolutely impossible for him to build a relationship built on terror."

She said that the young Fritzl was haunted by nightmares of growing up in wartime Austria where he was forced to descend into a dingy, dark air raid shelter for hours on end alone. She said he has a need for control, of events and more specifically, people. "He has suffered from this illness for decades and as long as he has a sex drive he will be in danger of re-offending," she said.

"He knew what he was doing was wrong but he had fantasies and these amounted to a feeling of 'I'm not allowed to but it would be so good...'

"The desire to own one person for himself became bigger and bigger. He had an ability to distance himself completely from reality. I asked him how he could possibly live this upstairs downstairs life and he said: 'It was simple. As soon as I left the cellar, it was gone.'

"But when he went to bed and woke up the next day he knew he was doing something that broke every rule in the book. He suppressed his feelings down into the cellar of his soul."

She said Elisabeth "was stubborn and strong and if you conquer someone who is stubborn and strong, that is more gratifying."

■Professor Jeremy Coid, head of forensic psychiatry at Barts and the London, writes: "For Fritzl, the intrusion into his private fantasy world is an unbearable form of torture. This is a man who is very private and has to be in control. Facing the court and the flashbulbs is like being stripped naked. So putting a folder in front of his face was like a figleaf for him - it's as primitive and simple as that. But a confession allows this whole process to stop. We shouldn't see this as an admission of remorse. Instead, it's a way of him regaining control, of retreating back to his cell away from public scrutiny where he feels more comfortable.

"Now he has confessed there is a possible risk of suicide. With someone as perverse as Fritzl, these compulsive sex acts are a form of anti-depressant. It makes him feel something. But a number of abusers develop a depressive illness after conviction because they have nothing left in their life."