London, July 18 : Austrian incest fiend Josef Fritzl's kids with his daughter have refused to testify against their dad.
Such a development could cause a setback of the case against him.
The 73-year-old Fritzl has confessed to imprisoning his daughter Elisabeth, 42, in a cellar dungeon beneath his home in the town of Amstetten for over 24 years, and fathering seven children with her.
One of the children died at birth in 1997 and Fritzl burned his body in an oven.
Elisabeth has completed testifying against her dad and reportedly reinstated her earlier statement given to police, in which she accused him of rape and abuse and for indirectly causing the death of her newborn.
But her two adult children, whose testimonies were supposed to be included in the charges, are said to have refused to give evidence, in accordance with their rights guaranteed by Austrian law.
"It is not clear when or if the two adult children will be questioned. It now appears possible that they could use their right not to make any statements," Telegraph quoted prosecutors' spokesman, Gerhard Sedlacek, as saying.
Fritzl selected three of his children with his daughter - Lisa, 15, Monika, 14 and Alexander, 12 - to live with him and his wife Rosemarie in their upstairs apartment, while the other three siblings - Kerstin, 19, Stefan, 18 and Felix, five - were left to dwell with their mother in the dank cellar never seeing the light of day.
Prosecutors want to use the testimonies of Kerstin and Stefan to reinforce the basis for the charges against their father.
Fritzl is facing charges of manslaughter for the baby that died, as well as rape, abuse, incarceration and incest.