VIENNA, Austria —  The Austrian man who held his daughter captive for 24 years and fathered seven children with her may be charged with slavery, a prosecutor said Monday.

St. Poelten prosecutor Gerhard Sedlacek also said authorities hope to have a series of formal charges ready by the end of September and that a trial would likely begin in December.

Investigators say Josef Fritzl confessed to taking his daughter Elisabeth prisoner when she was 18, sexually abusing her and fathering seven children with her, including one whose body he allegedly tossed into a furnace after it died. They say subsequent DNA tests confirmed he is the surviving children's biological father.

Fritzl could face murder charges — and a life sentence — if there is enough evidence to prove the infant he allegedly incinerated could have survived after birth had it received proper medical care.

Sedlacek said investigators have finished questioning Elisabeth and are now awaiting a report by a doctor who has been asked to try to determine how the infant died.

The prosecution is also waiting for an expert opinion on Fritzl's psychological state, Sedlacek said.

If found guilty of slavery, Fritzl could face 20 years behind bars.

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