A retired family doctor has been struck off the medical register after giving excessively high doses of morphine to 18 patients.
Among them was 74-year-old oesophageal cancer sufferer Harry Gittins who died on 22 January 2004.
In an interview with the Daily Telegraph, Dr Howard Martin said: "I told him I could make him comfortable at home and that's what he wanted. That was his choice. I did shorten his life."
But Mr Gittins could have gone on to recover had Dr Martin not intervened with 200mg of diamorphine, a General Medical Council hearing was told.
Mr Gittins's son, Paul, has now spoken of his shock at hearing his father was going to die.
"My dad was not in any pain and discomfort that day. There was no reason for him [Dr Martin] to do what he did," he told the BBC.
"My dad had no intention of wanting to die, definitely not. I never thought for one minute that Dad was going to die," he said.
"I'd picked him up from hospital on the Friday, he'd walked to the car well. He was in fine spirits, he was actually really good.
"I went into shock when he said he was going to die."
He described how Dr Martin had arrived at his parents' home in Newton Aycliffe in County Durham, early in the morning, just as his father was preparing to go into hospital for dehydration.
"My mam wanted him to go into hospital and Dr Martin said 'No he'll stay here - he's my patient. I know exactly what to do with him," he told BBC News.
The doctor then gave him a dose of morphine which left him unconscious for the rest of the day, said Mr Gittins.
That evening the doctor returned to say his father would die that night, he added.
"He said 'I've had a letter from the hospital to say your dad's riddled with cancer. I haven't got it with me - it's on my laptop and your dad's going to die.'"
The GMC hearing heard the family were wrongly told the cancer had spread.
Further doses were administered that evening and Harry Gittins died the next day.
At a six-week trial the following year, Dr Martin was cleared of murdering Mr Gittins with morphine overdoses.
The prosecution at Teesside Crown Court alleged he had administered huge doses of powerful painkilling drugs with the intention of killing.
But the defence argued that the prosecution had failed to prove the doses of morphine and diamorphine had killed him, nor had the Crown proved Dr Howard knew exactly what effects the drugs would have.
Dr Martin was also found not guilty of murdering Stanley Weldon, 74, of Coundon Grange, and Frank Moss, 59, of Eldon, Co Durham.
On Friday, a disciplinary panel for the General Medical Council found Dr Martin had not acted negligently but had "violated the rights of the terminally ill".
Paul Gittins told BBC Radio 4's Today programme he hoped the police would reinvestigate his father's death using fresh evidence from the coroners' court and the GMC hearing.