A teenager has confessed to murdering a man he met in a homeless shelter and eating parts of his brain and internal organs.

The 19-year-old, named only as Robert A, is alleged to have killed his 49-year-old room-mate by crushing his skull with a 20lb (9kg) iron bar, before using a butcher’s knife to remove the man’s intestines.

The murder is believed to have taken place at least three days ago and was discovered yesterday when a cleaner entered the shelter. The man allegedly told her about the murder and asked her to inform the police.

Officers who arrived at the ground-floor flat in the 15th district of Vienna found the body lying in a pool of blood, with body parts spread around the room. Half-eaten parts were found on a plate in the kitchen.

The 19-year-old was sitting next to the victim, his clothes allegedly soaked in blood. He reportedly greeted the officers by saying: “Just look what happened here.” He is believed to have told them that he had quarrelled with the dead man.

A police investigator said of the scene: “We are supposed to be prepared for situations like this, but this surpasses the limits of imagination.” Officers who attended will receive counselling. The two men lived alone in the shelter, a two-bedroom flat that is run by a private social care company, financed partly by the city authorities. It was created as a first-aid accommodation for mentally ill people living on the street. The residents receive weekly visits from social workers.

Robert A was placed there this month; the other man, named as Joseph S, was registered as having been a resident since June.

Reinhard Haller, a psychiatrist who has studied cases of cannibalism, said that the alleged killer was most likely to be suffering from either “a severe psychosis or extreme sadistic urges”.

Professor Haller said: “There are two possible explanations for his actions that immediately come to mind: a psychotic reaction, triggered by alcohol or other drugs, or severe sadistic derangement. A psychotic reaction could lead to insanity, including hearing voices and other hallucinations, that could make the perpetrator feel as if he was guided by outside forces and not acting on his own.

“The second scenario is that the man was a severe sadist but has managed to suppress his urges until now. The reported quarrels with his victim could have unleashed the accumulated aggression. In both cases we are talking about highly abnormal conditions.”

In 2001 Armin Meiwes killed a man and ate his penis. The murder, in Rotenburg, Germany, was committed with the consent of the victim, who replied to an advertisement on the internet.

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