Josef Fritzl, 73, is suspected of imprisoning his daughter, Elisabeth, 42, in the cellar of his home for 24 years while he raped her several times and fathered seven children with her, The Times of London reported Friday.

Fritzel has been accused by his daughter of allowing their newborn son, Michael, to die before burning the corpse in a incinerator, The Sun reported.

The case against Fritzel weakened when it became known two of his children may not testify in the trial, which is expected to begin in the fall, The Times said.

"We still have not fixed a date for the questioning of the two adult children but it has now emerged that they could make use of their right not to speak to the authorities and refuse to give evidence against their father," prosecution spokesman Gerhard Sedlacek told The Times.