(CNN) -- Police, medical professionals and those who know Josef Fritzl are struggling to piece together how he led a double life for more than two decades in a small Austrian town.
Fritzl, 73, admitted imprisoning his daughter in the cellar of this building for more than two decades.
Those who knew Fritzl describe him in such contrasting terms -- friendly, reclusive, arrogant, a kindly grandfather -- that it seems no one really knew him at all.
At his home on Ybbsstrasse in the quiet town of Amstetten, east of Vienna, the 73-year-old retired electrician lived with his wife, Rosemarie, and the three children he has admitted to fathering with his daughter.
In addition to those three children, Fritzl fathered four other children with the now 42-year-old daughter he kept imprisoned in the cellar, police said.
The children were products of years of sexual assault Fritzl inflicted on her, police said. Two boys and a teenage girl were locked up with their mother in a basement dungeon. A seventh child he fathered with his daughter died, and Fritzl burned the infant's body, police said.
The three children who were locked up had not ever seen the light of day, investigators said.
Fritzl had been lying to his wife for years, telling her his daughter had dropped off the three children at the house because she could not take care of them, police said. In reality, Fritzl had forced his imprisoned daughter to write letters that made it seem that way. Police say Fritzl's wife was unaware of the other children in the cellar.
It was a deception he maintained from 1984 until just days ago.
Rosemarie Fritzl was unaware of her husband's crimes, police spokesman Franz Polzer said.
"Let me also add that we know the suspect not only possessed an increased sexual potency, he's also very dynamic, imperious and quite authoritarian in his conduct and relationship to his existing family," Polzer said Monday.
Polzer added that Fritzl made clear to his wife and the children living with them that the basement area was out of bounds. He bought food for his captives and took it to them at night.
Medical professionals have also offered their interpretations of Fritzl.
"What is chilling about this case is the cold, sociopathic detachment that Josef F[ritzl] went through year after year, decades even, to hide his crimes," said clinical psychologist Dr. Kristina Downing-Orr.
"It was as if there was no remorse, no empathy for his daughter, for his grandchildren, for his wife. That's what's chilling."
She said Fritzl, who his daughter has said abused her beginning at the age of 11, possibly didn't want the relationship to end when she turned 18. So he imprisoned her.
"Perhaps she would go out and have boyfriends of her own," Downing-Orr said. "Perhaps he was a bit afraid he would be caught, that she would go out and tell people, and that led him to imprison her in this dungeon basement.
"It's that chilling sociopathic methodology, that kind of logic, that I find particularly chilling," she continued. "But fortunately, it's very rare; we rarely see that kind of behavior."
Verena Huber, 14, went to high school with one of the children raised by Josef and Rosemarie Fritzl. Alexander Fritzl, 12, seemed to have no clue about what was going on.
"He always told us his mother was dead," Huber said, describing the boy as happy and normal.
The fact that Josef Fritzl lived reclusively didn't alarm anyone, most people in the small town say.
Karl Dallinger is in the Amstetten fire brigade, in which Austrian youth learn the basics of first aid and other survival skills. He also said Monika and Alexander Fritzl seemed normal.
"They were both always willing to learn," he said. "They were good kids, they seemed to be happy kids."
Their grandmother often came to fire brigade events with her grandchildren to help cook spaghetti for everyone, he said.
"People here say this is difficult to understand or accept because [the Fritzls'] reputation in this community was as the kindly grandparents for taking in these children and raising them," said CNN's Phil Black, reporting from Amstetten.
A woman in Amstetten, identified only as Gabriele H., told Austria's Kurier newspaper that she thought Fritzl was a devoted grandfather doing his best to look after his abandoned grandchildren.
"One who looks after their grandchildren whilst their mother just ran away. We were all asking ourselves, what kind of mother would do that to their children?" she said.
"Mr. Fritzl and I grew up together," Erika Manhalter, who lives a few meters from the Fritzl home, told Kurier. "We thought this would be a family just like others, but you cannot look through people." E-mail to a friend
CNN's Frederik Pleitgen contributed to this report.
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