Josef Fritzl, who repeatedly raped his daughter and fathered seven of her children, has pleaded guilty to murder at his trial in Austria. The 73-year-old told the court in St Poelten: "I plead guilty to (all) the charges in the indictment." He also altered his plea from "partial" to full guilt on the rape count. Fritzl had earlier admitted incest with his daughter Elisabeth, now 42, but denied murdering their newborn son in 1996. The infant, a twin, died three days after he was born and the prosecution had claimed the baby would have survived if Fritzl had sought medical assistance. He also admitted enslaving Elisabeth and her children in the windowless purpose-built soundproofed cellar under his home. She was kept there for 24 years. Defence lawyer Rudolf Mayer said he was "completely surprised" by Fritzl's plea change but said his client may have been overcome by Elisabeth's harrowing statement, screened at closed-door proceedings on Tuesday. "I believe that he has been really shaken," Mr Mayer said. "He saw his daughter on the video for the first time and I think that this could have brought about the change." Fritzl's turnabout also altered his plea from "partial" to full guilt on the rape count. Fritzl had earlier admitted incest but denied murder and enslavement, the two gravest charges, at Monday's outset of the trial in St Poelten, west of Vienna. The trial is due to finish on Thursday, with sentencing the same day. Fritzl expects to spend the rest of his life incarcerated, Mr Mayer said. The prosecution has asked that he be sent to a secure psychiatric hospital and the court could rule that he has to stay there indefinitely, irrespective of his sentence. However, under Austrian law, a confession can lead to a reduced sentence, court spokesman Franz Cutka said. "It all depends on whether the jury and the judges take the confession to be a mitigating circumstance," he said. After admitting he was guilty of murder, Fritzl told the judge he should have taken seriously the fact that the infant was breathing poorly and tried to get the boy to a hospital quickly. "I was hoping the little one would survive but I should have done something. I don't know why I didn't help. I just lost sight (of the issue)," he said in a low voice. The children who had never seen daylight had to watch Fritzl repeatedly rape their mother Elisabeth, according to the prosecution, who say he treated her like his own property. "The basic need was for power. It is about domination, about power, about control," psychiatrist Adelheid Kastner said in her testimony. "He is aware of his evil side." Fritzl's abuses came to light last April when he took the eldest child, 19-year-old Kerstin, to hospital after she became seriously ill. Elisabeth and her six children, three of whom were incarcerated from birth, are now living in an undisclosed location under new identities. Three of the children were raised above ground by Fritzl and his wife Rosemarie after he told people that Elisabeth had abandoned them and joined a sect. Police say Rosemarie had no knowledge of her husband's actions.