ST. POELTEN, Austria (CNN) -- Josef Fritzl, the Austrian man accused of repeatedly raping his daughter in a cellar dungeon for decades, has admitted guilt on all charges, including responsibility for the death of one of seven children he fathered by his daughter.
Josef Fritzl is seen without his face covered and surrounded by security guards Tuesday.
Fritzl had already pleaded guilty to incest and other charges, but previously denied charges of murder and enslavement.
But on Wednesday Fritzl told the court in St. Poelten, 70 kilometers (40 miles) west of Vienna, he had changed his mind after watching his daughter Elisabeth's video testimony earlier in the week.
In a weak voice, the 73-year-old said he was in the cramped cellar when the baby, called Michael Fritzl, was born.
He noticed the child was breathing heavily, he said, but did not think the baby would die and opted not to seek medical attention.
Fritzl told the court he was therefore probably responsible for the child's death. He had previously told police he had burned the baby's body in a furnace.
"This is a major development in this trial," said CNN's Frederik Pleitgen. "The murder charge is really the centerpiece of this whole trial because only a murder conviction could get Josef Fritzl a life sentence." Watch what Fritzl's new plea means for the case »
Fritzl's new plea could speed proceedings although the jury must still decide on his guilt or innocence, a court spokesman said. "The admission of guilt alone is not enough," spokesman Franz Cutka told reporters.
Observers had said the murder charge might be difficult to prove because the only evidence was testimony from Elisabeth and a neo-natal expert. A verdict had been expected on Thursday.
Wednesday's proceedings will involve psychiatrists talking about Fritzl and his daughter, and a technical expert who will testify about the construction and living conditions of the cellar.
The underground chamber had low ceilings -- about 1.7 meters (5.5 feet) high -- and, for the first couple of years, only minimal sanitation. The cellar had no daylight or fresh air.
On Tuesday, the court heard from one of Elisabeth Fritzl's brothers, Harald. The media and public were barred from the courtroom during his testimony. Authorities have said Elisabeth and her children were given new identities and are in a secret location. Watch second day of the Fritzl trial »
Prosecutors allege that Fritzl closeted Elisabeth in a specially designed cellar in 1984, when she was 18, telling other family members she had run away to join a cult. He kept her there for 24 years, authorities think, repeatedly sexually assaulting her and fathering her seven children.
Fritzl took three of the children upstairs to live with him and his wife, telling the family that the missing Elisabeth had dropped them off.
Elisabeth and the remaining children never saw daylight, prosecutors said, and Fritzl went away for long periods, leaving them without food. To punish them, prosecutors said, Fritzl sometimes turned off the power in the cellar for up to 10 days.
The case first came to light in April 2008 when Elisabeth's then-19-year-old daughter, Kerstin, became seriously ill with convulsions, and Elisabeth persuaded her father to allow the girl to be taken to a hospital.
When Elisabeth gained her freedom, she told police her father began sexually abusing her at age 11. Seven years later, she said, he drugged, handcuffed and locked her in the cellar.
Defense attorney Rudolph Mayer has said Fritzl expects to spend the rest of his life in prison.
Under Austrian law, murder carries a maximum sentence of life imprisonment. In cases where a defendant faces multiple charges their sentence will be determined by the worst crime of which they are convicted.
The charges Fritzl faces are:
• Murder: The infant who died in 1996 died from a lack of medical care, the state prosecutor said. The charge carries a sentence of life in prison.
• Involvement in slave trade: From 1984 until 2008, prosecutors allege, Fritzl held his daughter, Elisabeth, captive in a dungeon, abused her sexually and treated her as if she were his personal property -- in a situation similar to slavery. If he is convicted, the sentence could range from 10 to 20 years in prison.
• Rape: Between August 30, 1984, and June 30, 1989, Fritzl "regularly sexually abused Elisabeth," according to the prosecutor. The sentence could be from five to 15 years in prison.
• Incest: Parallel to the rape charge. It carries a sentence of up to one year.
• Withdrawal of liberty: Three of the children Fritzl had with Elisabeth were illegally held captive in a dungeon with no daylight or fresh air, according to prosecutors. That charge carries a sentence of one to 10 years.
• Assault: Between August 28, 1984, and April 26, 2006, Fritzl repeatedly threatened Elisabeth and their three children with gas and booby traps as warnings in case they tried to escape, authorities allege. The sentence would range from six months to five years.
CNN's Diana Magnay and Frederik Pleitgen in St. Poelten and Melissa Gray in London contributed to this report