London, May 16 (ANI): Austrian incest dad Josef Fritzl's threats to his cellar family that he would gas them to death if they tried to escape their underground dungeon were a mere bluff, cops have revealed.

The 73-year-old electrical engineer, who kept his daughter Elisabeth, 42, as a personal sex slave in a concrete bunker beneath his house for 24 years and fathered seven children with her, told his captive family that they would trigger a special mechanism and be poisoned by gas if they tried to escape.

He kept them in a constant fear of death also by telling them that they would be killed by an electric shock if they tried to open the steel door that imprisoned them in the 55-square-metre dungeon under his house in the town of Amstetten.

But after over two weeks of investigating the dungeon, police revealed that his threats were a bluff aimed to pre-empt any attempts of escape, as there were no gas pipes leading into family's subterranean dwelling.

Elisabeth Fritzl told police that she had been thinking about escape but never dared to attempt it for fears that she and her children would be poisoned by gas.

The heavy steel and concrete door to the dungeon, which weighs over 300kg and is operated by a remote-controlled electronic device, has not yet been inspected by police.

"The door will be inspected by specialists next week, but it is clear that the suspect displayed a high degree of professionalism when he assembled it," the Telegraph quoted Colonel Franz Polzer, the local police spokesman, as saying. (ANI)