The three Gold Coast women from the same family who took their lives obtained instructions from a how-to-die book and lethal gas from a home-brew shop, Australian euthanasia campaigner Dr Philip Nitschke said.
Dr Nitchke told 7 News the elderly mother and her two adult daughters on a luxury island north of Surfers Paradise had been followers of his campaign, but he denies supplying them with deadly nitrogen gas in the lead up to their deaths.
Known as "Dr Death", the Netherlands-based right-to-die campaigner told the Courier-Mail he has nothing to fear as the deaths were "totally legal".
A Queensland Police spokesman told 7 News Online the investigation had been handed over to the coroner, but while there were no plans to contact Dr Nitchke, it could not be ruled out.
Dr Nitschke said the gas the women reportedly used to suffocate themselves was bought from the home-brewing distributor based in Queensland.
The company's Australian website sells the nitrogen gas bottles for $1020, including a gas regulator.
The website states purchasers "must be 50 years and over" and ID is required.
"I believe they had access to it [nitrogen gas] but not from me," he said.
Dr Nitschke said he did not personally know the women but confirmed they had joined his Exit International group six months ago.
"They were not terminally ill people but on the other hand, they were not in the best of health either," he said, speaking from Amsterdam on Wednesday.
"They were obviously working out what they wanted to do."
Dr Nitschke said the trio did purchase one of his black-listed books about euthanasia online and "clearly researched in particular detail".
"The only country my book is banned in is Australia," he told 7 News.
A Gold Coast man returned to the luxury residential estate of Ephraim Island at Paradise Point on Tuesday to find his wife, mother-in-law and sister-in-law dead.
It believed Margaret Cummins, 78, and her daughters Wynette and Heather, aged in their 50s, all had medical problems and their deaths are being treated by police as non-suspicious.
Detective-Senior Sergeant Mark Procter told News Corp police would not be providing further comment.
After the trio were found dead, the investigator said the husband was "not surprised" the women had taken their lives, adding "I think he's surprised it's three of them at once".
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