The case against Josef Fritzl, who imprisoned his daughter in his basement for 24 years, has suffered a further blow today after his children refused to testify against their father.

Fritzl, 73, is accused of incarcerating his daughter Elisabeth, 42, in a purpose-built concrete bunker in the cellar of his home in the town of Amstetten, where he fathered seven children with her.

One of the children, a baby boy called Michael, died shortly after birth and Fritzl burned his body in an incinerator.

Elisabeth Fritzl has already finished giving evidence to court authorities. While the details of her testimony have not been made known to the public, it is believed that she accused her father of rape and physical abuse, as well as responsibility for the death of her newborn child, who is thought to have died three days after birth because of the severe conditions in the dank cellar bunker.

But prosecutors told The Times that Elisabeth’s two adult children, who were supposed to provide key testimonies against their father and support their mother's allegations, are likely to refuse to give evidence.

“We still have not fixed a date for the questioning of the two adult children but it now emerges that they could make use of their right not to speak to the authorities and refuse to give evidence against their father,” the spokesman for the prosecutors, Gerhard Sedlacek, said

“The matter will be discussed between their lawyer and the judge in charge, but it has been suggested that they decline to give any statement.”

Fritzl, a retired engineer, has already made a partial confession and is facing charges of manslaughter for the baby that died, as well as rape, abuse, deprivation of freedom and incest.

However, prosecutors told The Times that the first two charges would be very difficult to prove because of a lack of forensic evidence, and that they were relying on the testimonies of the children to strengthen the charges against Fritzl.

Click here for more on this story from The Times of London.