Police on Tuesday inspected properties owned by a man who confessed to imprisoning his daughter for 24 years and fathering her seven children but said the man did not build any other secret hiding places.

Austrian authorities, meanwhile, said DNA tests confirm Josef Fritzl is the biological father of six of the surviving children.

• Click here to see photos of Josef Fritzl and the "House of Horrors."

Members of the Austrian family had an "astonishing" reunion at the clinic where they are getting psychiatric counseling, officials said Tuesday.

Authorities said the daughter, Elisabeth Fritzl, most of her children and her mother met each other Sunday morning at a clinic where they have been receiving psychiatric treatment and counseling.

"It was astonishing how easily it happened — how the mother and grandmother came together," clinic director Berthold Kepplinger told reporters Tuesday.

Kepplinger said the family members interacted very naturally — even though the three children who lived with their grandparents never met their siblings in the windowless cell.

Officials said one of the children, who is receiving medical treatment at another hospital, was not part of the reunion.

Police said they combed through Fritzl's other properties but found no other hidden windowless cells like the one where he had held his daughter — now 42 — captive since she was 18.

Forensics experts on Tuesday carted boxes of belongings out of the cell Fritzl constructed beneath his apartment in Amstetten, a working-class town 75 miles west of Vienna.

Police said Fritzl confessed Monday to holding captive his daughter, sexually abusing her, fathering her children and tossing into a furnace the body of one child who died in infancy.

Officials had said Fritzl faces up to 15 years in prison if charged, tried and convicted on rape charges, the most grave of his alleged offenses under Austrian law.

But prosecutors in Lower Austria said Tuesday they were looking into the possibility of charging Fritzl with "murder through failure to act" in connection with the infant's death. Murder in Austria is punishable by up to 20 years in prison.

Franz Polzer, head of the Lower Austrian Bureau of Criminal Affairs, would neither confirm nor deny Austrian media reports that Fritzl, 73, had had past run-ins with the law. "If there was an offense outside of the statute of limitations, I can't comment on this," he told the AP, refusing to elaborate.

Investigators say they believe Fritzl's wife, with whom he had seven other children, believed her daughter had run away to join a religious cult in 1984 and was unaware that she was living as a prisoner beneath her feet.

Fritzl's lawyer, Rudolf Mayer, said his client also was under psychiatric care. Asked whether he showed any remorse, Mayer said only: "I cannot say at this point."

Fritzl "is really hit by this. He is very serious, but he is emotionally broken," Mayer told the AP on Tuesday.

But prosecutor Gerhard Sedlacek said Fritzl was "completely calm, completely without emotion" when he was formally placed in pretrial detention Tuesday.

Austria is still scandalized by a 2006 case involving a girl who was kidnapped and imprisoned in a basement outside Vienna for more than eight years, and residents of Amstetten were puzzled as to how the Fritzl case could go undetected for so long.

"How is it possible that no one knew anything for 24 years?" asked Anita Fabian, a teacher in Amstetten. "This was not possible without accomplices."

The town's authorities authorized the construction of an addition to the apartment building that Fritzl owned and lived in, with a basement, in 1978, city spokesman Hermann Gruber told the Austria Press Agency. He said inspectors examined the project in 1983 — the year before the young woman went missing — and nothing looked suspicious.

Police said the surviving children are three boys and three girls, aged between 5 and 19.

Officials said three of the children — aged 19, 18 and 5 — "never saw sunlight" until they were freed a few days ago.

Police released several photos showing parts of the cramped basement cell, with a gaily decorated small bathroom and a narrow passageway leading to a tiny bedroom. Investigators said an electronic keyless-entry system apparently kept Elisabeth from escaping.

The other three children lived with the grandparents. Fritzl and his wife registered those children with authorities, saying that they had found them outside their home in 1993, 1994 and 1997, at least one with a note from Elisabeth saying she could not care for the child.

Officials said social workers made regular visits to the family but found nothing out of the ordinary, reporting that Fritzl's wife was attentive, the three children were doing well in school and clubs, and that all of them played musical instruments.

Leopold Etz, a regional police official, told APA that Fritzl apparently chose which of the children would live upstairs with him and his wife according to whether they were "crybabies."

Etz said he could not confirm Austrian media reports Tuesday alleging that Fritzl took several "men's vacations" to Thailand with unidentified German friends in the 1990s.

The case unfolded after the eldest of the secret children, a 19-year-old woman, was found unconscious and gravely ill on April 19 in the building and was taken to a hospital. After receiving a tip, police picked up Elisabeth and her father on Saturday near the hospital. Fritzl freed the captive children the same day, Polzer said.

Hospital officials said the 19-year-old remained in critical condition Tuesday because of the effects of lack of oxygen, and was undergoing dialysis.

Amstetten Mayor Herbert Katzengrueber told AP in an interview that Fritzl was personable and well-liked, and that the town had honored the suspect and his wife in 2006 on the occasion of their 50th wedding anniversary.

Katzengrueber said he was at a loss to explain how such an atrocity could happen.

"No one can really explain it," he said. "I am appalled and saddened that such a thing could happen in my hometown. ... These have been awful and sad days."