The 36-year-old suspect, named only as Milan A., is reportedly an ex-convict who was released from a prison for offenders with psychiatric problems after what was thought to be a successful rehabilitation.

Milan A. was visiting his father (55), stepmother (52), and 14-year-old step-brother at their home, together with his wife and 11-year-old son. At around 10pm he attacked the older couple with a kitchen knife. They died before the emergency services arrived.

Milan A’s wife was also stabbed several times, but survived. The two children were reportedly in another room but witnessed the attack, and were not harmed. “The 14-year-old boy called the police,” police spokesman Markus Haindl said.

When police officers arrived at the house the suspect climbed out of a window, holding on to his son, who he threatened to stab if the police came near him. But the 11-year-old boy was able to free himself and run off, and police fired a warning shot at Milan A., who then dropped the knife. He was arrested immediately afterwards.

His wife was taken to Vienna General Hospital and given emergency surgery. Haindl said she is now in a stable condition.

Police said it’s unclear what Milan A’s motive for the attack was, and that so far interrogations had been “inconclusive”. Detectives say he could be suffering from a mental illness.

A neighbour of the dead couple, Willi N., told the Kurier newspaper that he was shocked by Saturday’s events. “I know the family and they’ve always been nice neighbours. It's all very dramatic.”

A neighbour of Milan A. also said that he was shocked and never would have believed he was capable of such a thing. He said that Milan had been behaving strangely in the past few days.