The son of a prominent Swiss art dealer is in police custody after the death of a 23-year-old man at the family's villa on Zurich's posh Gold Coast.

The 29-year-old alleged assailant, also an art dealer who specializes in Pop and street art, was a friend of the victim, according to reports.

It is unknown why the two were at the villa. Other members of the art-dealing family were away on holiday. The victim was found with fatal head injuries on the morning of Dec. 30 after the alleged assailant called police.

An investigation is underway and no motive is known although some reports suggest an argument led to the fatality. The assailant "basically admitted" to the crime said the local prosecutor in a 20 Minuten report on Monday.