AUSTRIA-DNA test results have confirmed that a monster who locked up his daughter for 24 years in a windowless cellar is the father of her six children.

Twisted Josef Fritzl, 73, was placed on suicide watch after appearing in court to answer charges of imprisoning his daughter Elisabeth, now 42, and repeatedly raping her.

“The DNA tests provided decisive evidence that the six children that Elisabeth gave birth to have the same father. We’re talking about Josef Fritzl. You can be sure that this man left nothing undone in order to deceive the family, his wife, the relatives, the children and everybody around him. He had no scruples to use every possible means to deceive the public and cover up his crime." - Austrian chief investigator Franz Polzer

To hide his daughter’s disappearance, Josef forced Elisabeth to write letters saying that she had run away to join a cult and didn’t want to be found.

During her 24 years in confinement Elisabeth gave birth to seven children, but one of them died shortly afterwards because of a lack of medical attention in the underground cell where Mr Fritzl hid his family and had her body burned.

Three of the surviving children had never left the three cramped underground rooms where they were held and remarked in wonder upon their release at seeing the moon for the first time.

Three other children were legally adopted by Fritzl and lived with him and his wife Rosemarie upstairs in the family home, totally unaware of the fate of their siblings imprisoned in the cellar below.

The children and their mother, are now facing several weeks of treatment after their release. Most of the children are said to be recovering relatively well, but the eldest, Kerstin, 19, remains in a coma after falling ill.

Mr Polzer told assembled journalists today that there is no indication so far that Mr Fritzl’s wife was an accomplice to the crime. Rosemarie Fritzl broke down in tears and hugged her estranged daughter upon being reunited with her at at the Mostviertel psychiatric clinic. Elizabeth and two of her children Stefan, 18, and Felix, five, who had never seen daylight before, met her three other children Lisa, 16, Monika, 14, and Alexander, 12, who were taken out of the prison at birth and have lived ordinary lives.

"They all met together at the hospital last night. It was a very touching moment, very dramatic and very emotional for all of them. There were tears and the ones who had been in the cellar were afraid. It was very hard for them. They are not as articulate as their siblings but they were able to express themselves and it was a happy moment." - A police source

Fritzl admitted holding Elisabeth captive in a dungeon excavated under his home in the quiet town of Amstetten. He also admitted to fathering seven children by her, and allegedly admitted burning the body of the seventh child in an oven.

Fritzl is due to appear before a judge today in St Poelten, the provincial capital of Lower Austria province.

Police have been inspecting other properties owned by Mr Fritzl, saying they wanted to ensure he was not holding any other captives. Incredibly, Fritzl told his interrogators he had imprisoned Elisabeth at the age of 18 to protect her from falling into a life of drugs.

A police source said: "He had a very long interrogation and he has confessed but he has showed no remorse for his victims. He is a very arrogant man."

He allegedly told police: "I locked Elisabeth up to hide her away from drugs. I wanted to save her from drugs and from herself. She was a difficult child."

When Elisabeth was interviewed by police she described how her father had "shackled her like an animal" in the dungeon, a police source said.

Guenther Moerwald, head of St Poelten prison, said Fritzl was completely calm when he arrived there yesterday and had been put in a large cell where he is constantly monitored. The electrical engineer and businessman faces charges of incest, abduction and imprisonment and could serve 15 years in jail if convicted.

The case unraveled when Kerstin fell ill and Fritzl took her to hospital. He then brought Elisabeth and her remaining two children out of the cellar, telling his wife that their "missing" daughter and her children had chosen to return home.

Albert Reiter, the doctor treating Kerstin, said her condition was critical and her artificially induced coma would continue for several more days.

"Our patient is in a severely life threatening condition which resulted from a lack of oxygen caused sometime between Wednesday and Friday when she was admitted. In addition to 20 years underground, 20 years with no sunlight, 20 years of psychological stress, come other factors like infection." - Dr. Albert Reiter

Fritzl kept his prisoners in a concrete dungeon that was less than 60 square metres and contained a padded cell.

Authorities have been asking how events in the house, situated in a busy street with shops passed unnoticed for so long.

Franz Prucher, head of security in Lower Austria, said: "Down in the cellar there it is just chaos at the moment. We have to go over every detail very carefully."

Fritzl was convicted of sexually assaulting a woman in the 1960s and had spent time in prison, a police source said. He also had another conviction for arson.

Meanwhile Alfred Dubanovsky a former tenant - who lived above Josef Fritzl’s sex dungeon - told yesterday how he could have rescued his victims 13 years ago – but dismissed knocking he heard coming from the pit of despair.

“I wish to God that I could turn back the clock. The signs were all there but it was impossible for me to recognise them. Who would ever believe something so terrible was going on right under my feet. It is a regret I will have to live with for the rest of my life.” - Alfred Dubanovsky

The petrol pump attendant spent 12 years in a flat Fritzl rented out on the lower floor of his home in Amstetten, Austria – moving out a year ago. He told how he kept hearing strange noises from the cellar – and watched his landlord ferrying wheelbarrows of food to it in the dead of night.

Fritzl warned his tenants the cellar was strictly off-limits – and anyone going near it would be thrown out.

“I lived there for 12 years and all the time that poor family was suffering so much down below. It is too awful to think about.

There were many things I found strange but I never would have guessed what they represented.

Herr Fritzl banned any of the tenants of the eight flats from going anywhere near the cellar or back yard.

He told us the cellar was protected with a sophisticated electronic alarm, and whoever went there would have their contract cancelled without notice.” - Alfred Dubanovsky

As more than 500 townsfolk in Amstetten held a candlelit vigil for the victims, Alfred went on:

“He used to take food and shopping down there in a wheelbarrow – always at night.

At other times I remember I could sometimes hear a knocking from the cellar that I couldn’t explain.”

But he believed the landlord’s assurances that the underground chamber was empty.

I never in my wildest dreams thought he was behind anything like this. He spent every day in his cellar but I thought his behaviour was pretty normal.” - Alfred Dubanovsky

Alfred had no idea that all the time his landlord’s sex slave daughter was surviving on supplies he had left for her – as were three of her children. The ex-tenant said of depraved Fritzl: “He would fly into a panic at the merest mention of the police or the law. When I moved out there was a dispute over who should pay for repairs to a door. I threatened to sue. He went pale and caved in immediately.”

Anita Lachinger, 32, who briefly rented the flat above Alfred’s, said that while she too was warned to steer clear of the cellar, the news about the Fritzls was impossible to believe.

“The Fritzl family made a very nice impression. The news about Mr Fritzl is incomprehensible to me.” - Anita Lachinger

This is the second dungeon found in Austria in the past two years, with a girl recently escaping from 8 years of captivity in an unrelated Austrian dungeon. Locals are beginning to wonder just how many of their neighbors have cellars containing incestual sex slaves.

Related: Girl escapes after being held in cellar for 8 years (TimesOnline)