Calculated planning led up to the suspected murder suicide of a family in Sydney's north with investigators tracing the gas used in the tragedy to an order placed weeks ago.
As the Colombian family of Maria Claudia Lutz, 43, prepare to arrive in Australia in order to take their loved ones back home, police are slowly piecing together what led to their deaths.
It is understood Mrs Lutz's husband Fernando Manrique, 44, had set up an account with a gas company, that allowed him to order carbon monoxide in recent weeks.
After the gas was delivered, understood to be to an address that wasn't his home, the tanks were kept outside his property, unbeknown to the rest of the family what it would eventually cause.
Questions are likely to be raised about the accessibility of the dangerous gas. It was available for purchase online through the company but the page has been pulled from its website.
The company declined to comment when contacted on Friday.
On Monday morning, Mrs Lutz, a devoted mother and volunteer at her childrens' St Lucy's school in Wahroonga, failed to turn up to canteen duty.
Her children, Martin, 10, and Elisa, 11, weren't in class either and calls to Mrs Lutz went unanswered, prompting a close friend to call police.
When two officers arrived at the Sir Thomas Mitchell Drive property at 11.30am they found all the windows and doors closed.
After forcing their way in, the officers found the bodies of Mrs Lutz, Mr Manrique, Martin, Elisa and the pet dog.
The fans were still spinning in every room and the odourless gas inside not immediately noticeable.
Later police discovered tubes in the roof cavity with gas leaked through the ceiling in what investigators are treating as a "deliberate act".
Police sources heavily doubt Mrs Lutz had knowledge of the suspected murder suicide.
As the heart breaking tragedy was being planned, Mrs Lutz, a resilient and strong woman, was happy and excited with life, friends told the ABC this week.
The disability support assistance for her two children, who had moderate intellectual disabilities, including autism, had been increased, aiding the mother in her care for them.
On Friday she met with her close group of friends and fellow mothers from St Lucy's for their weekly coffee date.
The next evening her husband was seen working on a gazebo in the front yard of their home. Sometime between Saturday night and early Monday, gas was pumped through the home.
In a bizarre backtrack this week, euthanasia campaigner Philip Nitschke was forced to correct his claim that Mr Manrique downloaded an euthanasia handbook from his organisation Exit International's website.
Dr Nitschke initially said that Mr Manrique obtained the handbook, called The Peaceful Pill, which contained a chapter about using carbon monoxide.
But that was later changed by Dr Nitschke after he checked his database.
He said he found it was not Fernando Manrique but another man with the same surname who downloaded the book, which is banned for sale in Australia.
Police have seized computers from the Davidson home but it is understood they have not found any such handbook.
Police are preparing to speak with Ms Lutz's parents, when they arrive in Sydney from Bogota in Colombia early next week.
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