Fernando Manrique waited until his wife and two children went to sleep before unleashing a lethal gas into their home, intending to kill them all in a "selfish and arrogant act".
The 44-year-old Sydney father chillingly planned his family's murder - ordering two cylinders of carbon monoxide and having them delivered to a friend's home - after his wife, Maria Lutz, told him their marriage was over and he needed to find somewhere else to live.
A fortnight later the bodies of the devoted mother and her children Elisa, 11, and Martin, 10, were found in their beds alongside the family dog Tequila.
Mr Manrique was found lying face down in the hallway. All five had died from carbon monoxide poisoning.
At the time of the deaths, Mr Manrique was heavily in debt and had a teenage girlfriend who lived in the Philippines.
But deputy state coroner Elaine Truscott on Friday ruled Mr Manrique's death a suicide, with "no evidence he intended to survive" and emphasised he'd acted alone in killing his family.
The finding was small comfort for Maria Lutz's friends who gathered outside Lidcombe Coroners Court wearing brightly coloured scarves designed by Elisa.
"It was a selfish and arrogant act and I can't understand it," friend Sarina Marchi told reporters.
Ms Lutz's friends say their grief was compounded by cruel speculation that she may have been involved in the deaths of her children who had autism.
The group said Ms Lutz's openness in speaking about her children's autism was used against her.
"A lot of people spoke about the burden of having children with disabilities but we don't see it that way and Maria didn't," Ms Marchi said.
"It's a massive responsibility but it's a responsibility she took up with great gusto, love and passion. She didn't deserve this, her children didn't deserve this."
The coroner on Friday said four artworks created by Elisa and Martin were a stark reminder of the potential cut short by their father's actions.
"Those paintings are beautiful and gave me pause to think of the gifts and contributions the Manrique children would have given due to the nourishment and opportunities their mother, friends and carers provided them," she said.
"But their lives were stolen by someone who should have been their protector and provider. I have no doubt that Fernando loved his children which I suppose is evidenced by his method of taking their lives."
Ms Truscott said despite the "painless" deaths inflicted on Ms Lutz and her children the tragedy was one of family violence.
She said Mr Manrique had a "possessive" attitude towards his wife and he struggled to accept she would have been fine without him.
"Maria and the children would, if left to live, have been more than happy on their own, indeed they would have prospered," she said.
"Fernando probably could not imagine how it would be for him on his own without her support and without the comfort of a family where he could come and go as he pleased."
The coroner has suggested delivery drivers be educated about the use of carbon monoxide and encouraged to report suspect deliveries.
The drivers who delivered the lethal gas thought it was "odd" it was being sent to a residential address.
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