Police are considering reopening an inquiry into a GP, cleared of murdering three patients, who admitted hastening the deaths of people in his care.
Dr Howard Martin told the Daily Telegraph he acted out of "Christian compassion".
He was struck off by the General Medical Council for giving excessive morphine to 18 dying patients.
Paul Gittins, whose 74-year-old father Harry was among them, said his father had "no intention of wanting to die".
Mr Gittins told the BBC: "There was no reason for him [Dr Martin] to do what he did."
Supt Paul Unsworth of Durham Police said the force's "immediate concern" was the impact on relatives.
He added: "A decision will have to be made on whether there are any new grounds on which to reopen the investigation and any such decision will be taken following consultation with the Crown Prosecution Service."
Friday's GMC disciplinary panel found Dr Martin had not acted negligently, but it did say he had "violated the rights of the terminally ill" and the retired 75-year-old was struck off for "completely unacceptable" treatment of some patients.
It said Dr Howard had acted on the "scantiest of evidence" of unbearable pain.
Dr Martin told the Telegraph that, in two cases, he hastened the deaths of patients without their permission.
"I twice helped people die, not because they wanted to die but because they had such dreadful suffering. Everyone else wanted to [die] - they could make that choice."
In an interview with the paper, he said: "There are times when you get called to people, maybe as a locum doctor, maybe as an emergency in their last day of life and you just don't have the time to go through all that formality.
"I have to treat the situation as I find it. My conscience is clear. I don't have anything to fear."
He went on to say he accepted that his confession put him at risk of "spending the rest of my life in prison" if police reopened his case.
One of those who he gave a final injection to was his son, Paul, 31, when he was dying from cancer in May 1988.
"A vet would put a dog down, but under the current system a doctor is not allowed to take positive action to help a patient in a humane way," Dr Martin told the newspaper.
Regarding his dying son, he said: "What more could I do for him other than make sure he had dignity?"
"I don't believe I've killed any patients. I believe I've made them comfortable in their hour of need. But I am deemed to be arrogant because I used my discretion.
"They want to extrapolate that to say I'm choosing to kill people. It's not like that. The patients are about to die and I want to make sure they are comfortable.
"How can a so-called caring society not understand that? How can I be reckless with someone who is about to die?"
Some relatives of Dr Martin's patients told the Telegraph he had betrayed their trust, others gave him their full support.
Dr Martin told the Telegraph he had decided to talk about what he had done to call for reform of care for the dying, which he claims confines the terminally ill to hospitals and hospices rather than allowing them the "dignity" of dying at home.
"The management of people that are dying I think is not good in our country, and I had personal responsibility for that and I used my discretion," he told the Telegraph.
"And I think that the public needs to discuss this and it shouldn't be a decision made by a few people who are controllers in this society like the politicians."
Dr Martin, a former Army doctor and police surgeon who qualified in 1958, said that during his three decades spent as a GP he had not hidden his views.
"I just promised people that they could die free from pain and with dignity," he said.
"Most times patients and relatives were of an accord and wanted the patient to be free from pain and have dignity. In that scenario, I would take control by keeping people asleep until they had passed over."
BBC medical correspondent Fergus Walsh said Dr Martin's admission that he acted without the consent of two patients meant that he was unlikely to win support even among those who want to legalise assisted dying.
Professor Steve Field, chairman of the Royal College of General Practitioners, said he was horrified and there was no excuse for hastening patients' deaths.
"What we try to do as GPs is support patients in their last hours, last days and if we're finding that the patients are suffering unduly, we can refer and get expert advice from our palliative care colleagues.
"I'm horrified that the doctor seemed to indicate in the interview that he actually hastened the death of two patients without their consent - I'm speechless."
The GMC's fitness to practise hearing in Manchester centred on the deaths of patients between 1994 and 2004 at surgeries in Newton Aycliffe, Shildon and Eldon.
It heard that Dr Martin had an "autocratic attitude" and believed he was always right.
It also heard that while some of the 18 patients might have had only days or hours to live, the deaths of some could have been hastened.
GMC panel chairman Professor Brian Gomes da Costa said: "Dr Martin's decisions to administer large doses of strong pain-killing drugs were made on the scantiest of evidence.
"There were many occasions when there was no clinical indication that the patient was suffering any pain.
"His record-keeping, including reasons for giving treatments, was appalling."
Dr Martin did not attend the hearing, and in a letter from his solicitor he said he had no intention of doing so as he did not intend to practise again.
In 2005, he was found not guilty of murdering patients Frank Moss, 59, Stanley Weldon, 74, and Mr Gittins.