ONE of the country's leading pathologists has told a murder trial that three of a GP's patients were not killed by high levels of morphine.

Dr Nathaniel Cary accepted that the deaths could have been hastened by the drug, but said they were not caused by it.

The Home Office pathologist was yesterday giving evidence on the 20th day of the trial of retired County Durham GP Dr Howard Martin.

Dr Martin is accused of murdering 74-year-old Harry Gittins, from Newton Aycliffe, in January last year, Stanley Wheldon, 74, from Coundon Grange, in March 2003, and Frank Moss, 59, of Eldon, near Bishop Auckland, four days earlier.

It is alleged Dr Martin, 71, who now lives in Gwynedd, North Wales, administered excessive doses of morphine to the three men "to help them on their way".

Dr Cary, who is also an independent forensic pathologist and has worked on some of the country's most high-profile cases, is the first witness to be called by the defence.

Yesterday, he was asked what should have been put on the death certificate of lung cancer sufferer Mr Moss, who was visited by Dr Martin and injected with morphine twice in the hours before he died.

Dr Cary said: "I think it is entirely possible that he was actually dying over the period of time prior to being given any morphine. He was in his dying phase. He had a terminal, incurable disease.

"It would not be appropriate to include morphine in the cause of death, otherwise we would include it for many people who die in hospices."

Asked by defence barrister Anthony Arlidge what part the drug played in Mr Moss's death, Dr Cary said: "It may have played a part, but if he was dying already you could not even be sure of that.

"One would have to look at the hypothetical situation that it may simply have made him die an hour earlier than he was going to die any way."

Dr Carey, who the court heard worked on the London bombings and the Soham murders, said it would be impossible to gauge what exact levels of morphine had been administered at the time.

And he told the jury that every person's tolerance to opiate medicine, such as morphine and diamorphine, was different.

"You simply cannot just grab hold of a level and say 'That's a lethal level'," said Dr Cary.

"It is a really bad mistake that has been made by some toxicologists over the years to talk about lethal levels."

Dr Cary also told the court that Mr Weldon, who suffered from dementia, could have been dying from pneumonia before Dr Martin administered morphine following a stroke.

Asked how plausible it was that the drug contributed to his death, the pathologist said: "It may have done, but not necessarily must have done."

Mr Gittins, who had throat cancer, had received chemotherapy and radiotherapy shortly before his death, and had contracted pneumonia. During three visits by Dr