Police in Austria have been detailing the elaborate lengths Josef Fritzl took to create the dungeon in which they say he incarcerated and raped his daughter.
Their assumption is that Mr Fritzl began planning the dungeon, which has eight separate doors, in 1979.
The family rescued from the house are getting to know each other again in their hospital quarters, police said.
The head of the jail where Mr Fritzl is being kept said the inmate had been no problem but refused to take exercise.
The head of the Lower Austria criminal investigation department, Franz Polzer, said Mr Fritzl had lodged a planning request in 1979 for an extension that became the centre of the secret dungeon.
At the time the daughter, Elisabeth, would have been 13.
At a news conference in Amstetten, west of Vienna, police said this showed Mr Fritzl may have had an “obsession” before 1984 to carry out the imprisonment and was able to deceive the family and others around him.
There was a section of the extension which served as the dungeon that was not known to the planning authorities.
The police said they believed Mr Fritzl had acted alone and were investigating claims from people who had come forward to say they had been raped by Mr Fritzl 30 to 40 years ago.
The daughter, Elisabeth, and six of her seven children by Mr Fritzl are together in a hospital quarters.
The eldest child, Kerstin, 19, whose serious illness and hospitalisation brought the alleged crimes to light, was said to have improved and stabilised.
However, she is still in an induced coma and will remain so for an unspecified time.
Prosecutors will have their first meeting with Mr Fritzl this Wednesday or Thursday.
Published on website of BBC NEWS