An Austrian court has overturned a lower court's ruling that 88-year-old incestuous rapist Josef Fritzl should be transferred to regular prison from a prison psychiatric unit.
The case has been sent back to the lower court for a new decision, it was announced on Monday.
Fritzl, who has now changed his name to one that has not been made public, raped his daughter and held her captive for 24 years, fathering her seven children.
The case attracted worldwide attention when it came to light in 2008.
He has been in a prison for "mentally abnormal" inmates since his conviction in 2009 for incest, rape, enslavement, coercion and the murder, by neglect, of his newborn son in a dungeon he secretly built under his house.
Fritzl applied for a transfer to regular prison, arguing that as an elderly, frail man he no longer poses any threat.
A court in the town of Krems an der Donau ordered the transfer in January, but prosecutors filed a complaint aimed at overturning that decision to the Vienna Higher Provincial Court.
"Unlike the court of first instance, the Vienna Higher Provincial Court came to the conclusion that the facts necessary for such a conditional release had not yet fully been established," the Vienna court said in a statement.
It said it had overturned the decision of the lower court in Krems and ordered the lower court to establish more facts before reaching a fresh decision.
Fritzl is suffering from advancing dementia but he was able to follow the brief proceedings in January when his conditional release was ordered, his lawyer Astrid Wagner told reporters after that hearing.
"A supplement to the medical report and a new hearing of the detainee at the end of April were ordered," a spokesman for the lower court in Krems said of the Vienna court's ruling.
From regular prison Fritzl would be able to submit a request to be released from prison altogether.
