"I 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, but still it became a normal occurrence to lead a second life in the cellar of my house," Josef Fritzl told The Times of London in a Vienna interview.

About the time he was turning his cellar into a cell with an idea toward a second family, daughter Elisabeth was becoming a problem, he said.

"Ever since she entered puberty she did not adhere to any rules any more, she would spend whole nights in dingy bars, drinking alcohol and smoking," he said. "That is why I had to do something; I had to create a place where I could keep Elisabeth, by force if necessary, away from the outside world "

He went on, "With every passing week in which I kept my daughter captive my situation was getting crazier. I really was thinking about whether I should let her go or not. But I was not able to make that decision, although -- or maybe exactly because of that -- I knew that with every passing day what I had done would be more severely judged.

"But I was afraid of being arrested and of having my family and everyone out there find out about my crime – and so I postponed my decision again and again," he said. "Until one day it was really too late to free Elisabeth and take her upstairs."

He said he then begun to compare his daughter to his mother: "But the urge have sex with Elisabeth was growing stronger and stronger." He added, "In reality, I wanted to have children with her."

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