A court psychiatrist yesterday described how Josef Fritzl had locked up his daughter as a way of compensating for a loveless childhood as she detailed his troubled relationship with his mother.

Adelheid Kastner told the court in St Polten that Fritzl was a dangerous man and recommended his transfer to a psychiatric institute for intensive therapy for a serious personality disorder. She said if it was left untreated even at his advanced age, Fritzl could go on to commit other crimes so great was his "need to dominate and control other people".

Kastner said Fritzl had developed strategies to learn to cope with life, including "pushing his feelings into the cellar of his soul". She said there was "much of the volcano about him," explaining that violent sex had provided the main outlet for his pent-up feelings. She said he had told her: "I was born to rape".

In an hour-long testimony to the court, based on extensive interviews she carried out with Fritzl last year, Kastner said that his behaviour had its roots in his troubled childhood, describing a mother who did not love him, who left him to cry when he was in pain, who regularly beat him and left him on his own for hours at a time. "Herr Fritzl spent most of his childhood in a severe state of anxiety," she said.

She described how his mother Maria, who herself had been fostered as a child, had had him "solely in order to prove to the world that she was not infertile" following a marriage which broke up because it produced no children.

"Herr Fritzl was a 'proof child', an 'alibi child'," she said, adding that this "was his only function as a child". "As a consequence he was a burden to her, something she was forced to look after". She said that Fritzl, now 73, struggled throughout his childhood to form a relationship with his mother but that "it was impossible to build up any sort of bond of trust with her".

The fear he felt by her constant absences was never more intense than during the second world war bombing raids on their home town of Amstetten. She refused to take refuge in the air raid shelter near to the family home, insisting on staying in the house and sending her son into the underground shelter instead. "As a result he suffered from an overwhelming sense of anxiety, not knowing when the air raid was over whether or not the only person in the world to whom he had any relationship, would still be alive," she said. "It's the type of fear that over time has a huge impact on a person".

She described how his mother ignored his screams when, as a young boy he suffered from the extremely painful, but easily treatable condition of phimosis, or a tight foreskin. Only the intervention of a neighbour prompted her to take him to see a doctor.

Fritzl listened attentively as Kastner delivered the in-depth psychiatric analysis of his character to the court. But at times he appeared nervous, twisting his fingers and his left foot, while glancing at the floor.

His decision to lock up his daughter stemmed from a need to compensate for the years during which his mother dominated him. "He developed an overwhelming desire to exert power - to dominate, control and possess another person. These were fantasies that grew and grew and which he managed to realise".

She said one reason as to why he chose Elisabeth, his fourth of seven children, was because of her resistance. "If you conquer someone you consider strong and stubborn, the effect is all the more gratifying". He told her he had chosen Elisabeth "because she was most like me, as strong as me, as stubborn as me".

She said that the more incestuous children he had with her, the more powerful he felt. "The more children, the more power he had over his victim". She said Fritzl was able to separate his two lives - the family he kept downstairs, and his official upstairs family.

"When I asked him how he was able to lead a double life, he said it was very simple. 'As soon as I went upstairs the downstairs family didn't exist any more'." But he told her that when he woke up in the mornings he was flooded with feelings of guilt, "realising that he was breaking every rule in the book".