Mystery surrounds the death of an Oxford University student who died minutes after chatting to a friend.

Christ Church undergraduate chemistry student Reignolde Mahboubian-Jones, 20, went to London for a rock concert the night before he died, on November 10.

An inquest in Oxford heard yesterday how fellow student Dale Phipps knocked on his friend's bedroom door the following day to wake him, as they had a tutorial at 10.30am.

Mr Phipps said: "He sounded as though he'd just woken up. We couldn't remember if our tutorial was at 10.30am or 11.30am, so he asked me to check before he got up." Mr Phipps said a few minutes later he heard strange noises from Mr Mahboubian-Jones's room.

He said: "I thought he'd gone back to sleep and was having a nightmare."

When he and another student, Edward Hall, tried to rouse their friend at 10.15am they found him slumped in bed and his pulse had stopped.

Mr Hall, of Leamington Spa, told the inquest: "We didn't know what was wrong. He didn't smoke or drink and didn't take drugs."

Reignolde's father, Malcolm Mahboubian-Jones, said that since his son's death he and his family had undergone tests to see if a genetic factor was responsible. So far, the research had proved inconclusive. He said it was impossible to see if there was anything inherited from his wife, as she had committed suicide three years ago.

Mr Mahboubian-Jones's body was examined first by Dr Peter Millard, a pathologist at Oxford's John Radcliffe Hospital, and Home Office pathologist Dr Nicholas Hunt.

Neither doctor could pinpoint the reason why the student died. Police found no suspicious circumstances.

Recording a verdict of death by natural causes, Oxfordshire coroner Nicholas Gardiner said the death remained unexplained. The coroner said: "He seems to have been a normal, fit, young man."