An international manhunt is under way for an Austrian pensioner who is believed to have killed his two siblings and their spouses after a dispute over his rent.

Josef Branis, 66, a retired bricklayer, is suspected of shooting his brother and sister and their partners in their homes. Police discovered the bodies shortly before midnight last night, after Mr Branis’s daughter found his blood-stained trousers in her house.

The shootings took place in Strasshof, the quiet town near Vienna where Natascha Kampusch was imprisoned in a cellar for eight years.

Austrian authorities announced this morning that Mr Branis was on the run and believed to be armed and dangerous. A large-scale search was initiated, including an international arrest warrant and involving the elite special police unit Cobra.

Mr Branis, a father of four, is believed to have fled the scene of the crime on a bicycle and then gone to his daughter’s house to change clothes. Police think that he rode his bike to the nearest railway station and may have gone into hiding in Slovakia.

The victims, Anna J, 63, Mr Branis’ sister, and his brother Franz, 65, were found dead with their spouses Johann, 67, and Vera, 59, in their homes in Strasshof.

Police suggested that the murders were motivated by an argument that began when Mr Branis’ sister Ana J increased the rent he paid to stay in her flat in Vienna. The quarrel escalated after Mr Branis took legal action a year ago and he was ultimately forced to move out of the flat on Monday, one day before the murders.

Leopold Etz, the chief inspector investigating the case, told Times Online: “The suspect’s daughter found a letter by her father that testifies to his hatred of his siblings and their spouses, all because of the dispute that started with the increasing of the rent.”

Mr Etz suggested that the man may have fled from Austria. “He is unable to drive due to an eye condition and is believed to have taken a train at the local railway station following the murders. We know he had some friends in Slovakia and that is where he might have gone into hiding,” he said.

“The victims all have gunshot wounds and appear to have been shot several times. It appears that one of the women was killed with three shots and her husband with five shots. The exact circumstances of their deaths will be determined by forensic experts who are examining the bodies and the scene of the crime.”

The suspected murder weapon, a 7,65 calibre pistol, was not found.

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