(CNN) -- An 80-year old Austrian man is being investigated for allegedly sexually abusing his wife and his two mentally disabled daughters for more than 40 years, police and a prosecutor said Thursday. The man's wife died three years ago, investigators said, but the daughters still lived with their father in the northwestern town of Braunau.  They slept on a wooden bench and were threatened by their father with a pitchfork, authorities said. "He isolated the two women from the outside world for all the time," said Ernestine Heger, one of the prosecutors in the case. Police freed the two sisters in May 2011, they said.  The man is in a nursing home in Braunau while the case is being investigated, authorities said.  Prosecutors now have to decide if they will order pretrial detention for the suspect. Austrian police discovered the abuse case by accident, they said. When the 80-year-old man fell on the floor in May, he was unable to get up.  His daughters refused to help him for two days. They then entrusted themselves to a social worker, who informed police about their allegations. The two daughters have not yet been questioned by prosecutors. According to Austrian law, they can refuse to testify. In 2008, Austrian Josef Fritzl was arrested after having imprisoned and raped his daughter for 24 years.  He was convicted on charges of incest, rape, false imprisonment, assault and murder and sentenced to life in prison in 2009.  The murder charge was for allowing one of the babies he fathered with his daughter to die shortly after birth. Heger said that in contrast to the Fritzl case, the sisters in Braunau "were not really imprisoned. "Although they could not move where they wanted, neighbors have seen them several times throughout the years," she explained. The two sisters are now in psychological care, officials said.
NEW:  The case was discovered through a social worker .
The 80-year-old man allegedly raped his daughters for 4 decades .
In a similar case in 2008, Josef Fritzl imprisoned and raped his daughter .
Fritzl was sentenced to life in prison .
(CNN) -- An 80-year old Austrian man is being investigated for allegedly sexually abusing his wife and his two mentally disabled daughters for more than 40 years, police and a prosecutor said Thursday. The man's wife died three years ago, investigators said, but the daughters still lived with their father in the northwestern town of Braunau.  They slept on a wooden bench and were threatened by their father with a pitchfork, authorities said. "He isolated the two women from the outside world for all the time," said Ernestine Heger, one of the prosecutors in the case. Police freed the two sisters in May 2011, they said.  The man is in a nursing home in Braunau while the case is being investigated, authorities said.  Prosecutors now have to decide if they will order pretrial detention for the suspect. Austrian police discovered the abuse case by accident, they said. When the 80-year-old man fell on the floor in May, he was unable to get up.  His daughters refused to help him for two days. They then entrusted themselves to a social worker, who informed police about their allegations. The two daughters have not yet been questioned by prosecutors. According to Austrian law, they can refuse to testify. In 2008, Austrian Josef Fritzl was arrested after having imprisoned and raped his daughter for 24 years. He was convicted on charges of incest, rape, false imprisonment, assault and murder and sentenced to life in prison in 2009.  The murder charge was for allowing one of the babies he fathered with his daughter to die shortly after birth. Heger said that in contrast to the Fritzl case, the sisters in Braunau "were not really imprisoned. "Although they could not move where they wanted, neighbors have seen them several times throughout the years," she explained. The two sisters are now in psychological care, officials said.
social worker, who informed police about their Austrian Josef Fritzl was arrested after having imprisoned and raped his daughter for 24 years. sentenced to life in prison in 2009.  The murder