British police say a post-mortem examination has not provided "obvious natural causes" for the death of a 23-year-old assistant to artist David Hockney.

A police statement said Wednesday that more tests will be needed to establish the reason for the death of Dominic Elliott. Results will not be known for several weeks.

Elliott was taken from Hockney's house in northeastern England Sunday morning and was pronounced dead in hospital. Police have said there were no signs of violence.

The 75-year-old Hockney is one of Britain's most famous artists. He had painted Elliott several times.