Defendant Josef Fritzl hides his face behind a file folder before his trial Monday at the provincial courthouse in St. Poelten, Austria.
Wearing a mismatched gray suit and hiding his face behind a folder as the trial began, Josef Fritzl pleaded guilty to incest and false imprisonment, but he denied enslaving his daughter Elisabeth or murdering her newborn son. He pleaded only partially guilty to additional counts of rape and coercion.
The 73-year-old Fritzl faces up to life in prison if convicted of the negligent homicide charge, which stems from the death of the 2-day-old baby boy, who investigators contend might have survived if he had gotten medical care. Incest, by contrast, carries only a one-year sentence.
A verdict could come as early as Thursday, officials said.
In her opening statement, prosecutor Christiane Burkheiser portrayed Fritzl as a callous and contemptuous captor who held his daughter in a cramped space that didn't have a shower or warm water and repeatedly raped her in front of the children.
At other times, Burkheiser said, Fritzl punished his daughter by shutting off the electricity — plunging the dungeon cell into darkness for days at a time.
"Josef Fritzl used his daughter like his property," Burkheiser said.
"The worst was ... there was no daylight," she said, adding it was also "incredibly humid" and the air was moldy and stale.
Burkheiser said Elisabeth was "broken" by Fritzl's alleged actions and the uncertainty of her fate and that of her children.
Three of the youngsters grew up in the underground cellar in the town of Amstetten, west of Vienna, never seeing daylight. The other three were brought upstairs to be raised by Fritzl and his wife, Rosemarie, who was led to believe they had been abandoned by Elisabeth when she ran off to join a cult.
Police say DNA tests prove Fritzl is the biological father of all six surviving children.
Fritzl's attorney, Rudolf Mayer, said his client regretted his actions and insisted he was "not a monster," even bringing his captives a Christmas tree.
"If you just want to have sex, you don't have children," Mayer said. "As a monster, I'd kill all of them downstairs."
Fritzl could face up to 20 years behind bars if convicted of enslavement and up to 15 for a rape conviction.
Court spokesman Franz Cutka told reporters the eight-member jury saw parts of prerecorded testimony from Elisabeth during closed-door proceedings Monday afternoon.
He declined to provide details or describe Fritzl's reaction, saying he was not present and that Austrian law prevented him from doing so.
On Tuesday, the court will hear more from Elisabeth's 11-hour videotaped testimony, Cutka said. It will also consider several reports from experts: one on Fritzl's psychological state, one on the newborn that died and one on the door leading into the dungeon. Cutka mentioned a possible fourth report but declined to elaborate.
The jury will also hear prerecorded testimony from one of Elisabeth's brothers, Harald.
Police imposed a no-fly zone above the courthouse to discourage news helicopters and prevent any attempted prison breaks from the jail next door where Fritzl has been in pretrial detention.
Mayer welcomed the security, saying both he and Fritzl had received threats.
As reporters lined up to enter the courthouse, a prominent Austrian comedian littered the area in front of the building with naked, bloodied dolls.
"If something like this is happening, something has to be changed on the legal level to give the victims better protection," said Hubsi Kramar, who has produced a satirical stage show about the Fritzl case.
The children, together with Elisabeth, initially recovered from their ordeal in a psychiatric clinic and then were moved to a secret location. To ensure their security and privacy during the trial, they have since returned to the clinic, where guards are on high alert.
The Associated Press normally withholds the names of victims of sexual assault. In this case, the withholding of Elisabeth's name by the AP became impractical when her name and her father's were announced publicly by police and details about them became the subject of publicity both in their home country and around the world.
Josef Leitner, one of Fritzl's former tenants, told AP Television News he's still shaken by revelations of what happened in the basement of the apartment building where he once lived.
"I hope (Fritzl) will get the punishment he deserves," he said.
Associated Press Writer William J. Kole in Vienna contributed to this report.