Nicola Davies QC, defending Dr Shipman, 53, asked him if he had injected 81-year-old Kathleen Grundy with diamorphine on 24 June 1998. "I did not," he said. Had he killed her?, she asked. "No I didn't," said Dr Shipman.
He said he was "suspicious" when he had an informal chat with Mrs Grundy about symptoms consistent with "codeine, pethedine or even morphine" abuse in November 1997. These included a bowel condition he could not cure, despite frequent prescriptions and tests.
"Abuse of drugs in the elderly is becoming recognised," Dr Shipman told the jury at Preston Crown Court. He said Mrs Grundy had arrived unannounced at his surgery in Hyde, Greater Manchester, on several occasions - once "when the cream cakes were being handed around" on his birthday - which explained why his consultations with her had not been logged in his appointments diary.
The pressures of running a surgery single-handed explained why his suspicions of her abuse had not been registered in his computer until after her death. "It's one of the problems about being a small practice - the patients can actually get to the doctor," he said.
He had handwritten notes to hide his suspicions from Mrs Grundy. "I wanted to be sure that if a time came when I did refer her, I gave a good history," said Dr Shipman, who stumbled over his words and and seemed nervous as he described the routines of surgery life.
It is the prosecution's case that he created a false medical history to cover his tracks after injecting all his victims with diamorphine.
Dr Shipman described how, at an 8am meeting at Mrs Grundy's home on the day of her death, he asked her: "Are you going to roll up your sleeve?" He was taking blood samples, because the previous day he had thought "she looked old ... going downhill." Dr Shipman sighed as he said she looked older than ever as he took her blood. He said he took her blood early that morning because it was imperative that the samples be examined within six hours.
Yet a plastic bag containing them became covered with letters and magazines in his consulting room and, amid a busy morning schedule, he overlooked them. He later decided that new samples must be taken, so threw out the old ones. (The court heard earlier that he told police he had sent them to a hospital pathology laboratory.)
He returned to Mrs Grundy's house after a bleep message informed him of her death. He made no effort to remove her clothing, because two elderly men were in the room but listened to her heart "almost for show", though he was sure she was dead.
"The problem was what had she died of. I thought old age might cover it," continued Dr Shipman. In a brief telephone conversation the coroner's office said this was acceptable, he said. Dr Shipman described how, during a consultation 16 days before her death, Mrs Grundy asked him to witness a document. He joked that if money was being bequeathed to him, he would not sign it. "There was a moment's pause" as he realised it was, so asked two patients to witness it.
In the witness-box, Dr Shipman folded a piece of paper into three and, by pushing it across the ledge of the box, demonstrated how he might have left fingerprint marks on the document as he pushed it across his desk.
He denied forging a pounds 386,000 will in Mrs Grundy's name. "Until it was shown to me, I had no knowledge of it whatsoever," he said. Mrs Grundy, he said, had borrowed his typewriter, on which the will was typed "two or three times".
Dr Shipman grew more confident during his four hours and 20 minutes in the witness-box. Initially, as he stumbled over his words, he said: "I must apologise. I slur my speech sometimes with the tablets I'm on." He declined Ms Davies' offer of water. She later asked him to speak more clearly.
Dr Shipman was watched by his wife Primrose, 52, and second-youngest son, David, as he gave evidence.
He confirmed details of his education and early career as a general practitioner at the Donnebrook practice, also in Hyde, where his patient list grew from 2,000 to 3,000.
He left and set up alone, because "other doctors were not as committed as I would have been to make fundholding work." He told how he had thrown himself into the conversion of premises into his own surgery - "I made sure I was involved in the work" - and, unlike other GPs, insisted on doing inoculations himself. He was also "one of the few doctors in the area who still handwrites letters. I never quite got word processing right."
The trial continues.