Euthanasia advocate Philip Nitschke has done an about-face, going back on earlier claims the Manrique-Lutz family - found dead in their home on Monday - had purchased his suicide how-to guide.
The bodies of Maria Claudia Lutz, 43, Fernando Manrique, 44, and their children Elisa, 11, and Martin, 10, were found on Monday morning after the children didn't show up for class and Ms Lutz didn't turn up to work. The house was completely sealed.
Police later found a network of pipes in the ceiling linked to two bottles of deadly carbon monoxide gas, leading investigators to suspect the deaths were a deliberate act.
Dr Nitschke told newspaper The Australian his group Exit International had "some contact" with the Manrique-Lutz family, and they had purchased The Peaceful Pill Handbook, which is banned in Australia.
But after checking his database, he now says they didn't.
"Fernando Manrique did not access our book," he told Australia radio station 2GB on Thursday. "[It was] a person of that surname but it was a different Christian name [that] made contact trying to acquire the book."
Dr Nitschke said Exit International has never knowingly advised an entire family on how to end their lives, and wasn't about to start.
"Obviously if that did happen, we would be very cautious," he told The Australian.
Police believe it was a murder-suicide carried out by Mr Manrique. He was recently seen on the roof of their house "banging and hammering", according to neighbours.
Meanwhile Ms Lutz was in good spirits leading up to her death, having just met with a team from the National Disability Insurance Scheme. Both Elisa and Martin were autistic, and had complex needs.
She had also just finished earning a teaching degree.
Even before realising he hadn't sold the family The Peaceful Pill Handbook, Dr Nitschke sought to distance himself and Exit International from the tragedy.
"People buy the book and we don't get to know them. And obviously this is a tragedy, although that sounds like I'm critical of them, which I'm not," he told the paper.
"Obviously parents sometimes get taken to extreme levels of stress, and it’s hard to be critical. It's easy for us to sit here and say we are critical.
"We are not going through the situation they are going through. I agree it's a tragedy, but until you walk in their shoes, it's very hard to be critical."
With the family's Colombian background, Dr Nitschke said it surprised him they didn't use pentobarbital, used in lethal injections in the US under the brand name Nembutal.
"Bogota is one of the few places where you can obtain the euthanasia drug Nembutal and we say that in the book, so it was interesting to see they used carbon monoxide.
"Using carbon monoxide is a very peaceful and reliable death. If you do know what you're doing, it's very effective."
He compared the incident to a Canadian case from the early 1990s, in which farmer Robert Latimer used carbon monoxide to kill his daughter Tracy, who had severe mental and physical disabilities.