Cellar dad Josef Fritzl revelled in "playing God" with other people's lives, say psychiatrists.
The 73-year-old's demented love of power was probed by psychiatrists on May 13.
"He enjoyed being the master of life and death. He's the personification of the terrifying power of evil - the devil," the Mirror quoted Psychiatrist Christian Ludke, as saying.
Dr Ludke said that the electrical engineer was emotionally abused by his mother. He said: "That's why he became an abuser. He had sick fantasies. He couldn't take revenge on his mother. So he wreaked it on his own children."
Fritzl fathered seven children by daughter Elisabeth, 42, who he kept captive in his cellar for 24 years.
He is held at St Poelten jail, 60 miles from his home in Amstetten, Austria.
The psychiatrists will decide if he is fit to stand trial or criminally insane.
Elisabeth is still waiting to visit 19-year-old daughter Kerstin, in a coma in another clinic.
