A cancer patient allegedly murdered by his doctor with an overdose was already close to death, a court has heard.
Dr Howard Martin has declined to give evidence at his trial
Dr Nathaniel Carey, a pathologist, told Teesside Crown Court that Frank Moss, 59, of Eldon, Co Durham, would have died regardless of any overdose.
Dr Howard Martin, 71, denies murdering three men including Harry Gittins, 74, of Newton Aycliffe and Stanley Wheldon, 74, of Coundon Grange, both Co Durham.
The GP, of Penmaenmawr, North Wales, has declined to give evidence.
Dr Carey, a Home Office pathologist, was the first witness to be called by the defence on Wednesday.
Dr Carey, who worked on the London bombings and the Soham murders, told the hearing it would be impossible to gauge how much morphine had been administered at the time of Mr Moss' death.
The GP has pleaded not guilty to all charges
He said: "Mr Moss was in a dying phase and had a terminal and incurable condition.
"Morphine may have played a part but if he was dying already, you cannot even be sure of that.
"One would have to look at a hypothetical situation that it may simply have made him die an hour earlier than he would have died anyway.
"It would not be appropriate to include morphine as a cause of death, otherwise we would have to include it for any people that died in a hospice."
Dr Martin has been accused of administering excessive doses of morphine to Mr Gittins, who died in January last year, Mr Wheldon, who died in March 2003, and Mr Moss, who died four days earlier.
Their bodies were exhumed after a police investigation prompted by family concerns.
The trial continues.