Police have uncovered an elaborate system of gas pipes at the Sydney house where a family were found dead on Monday.
The bodies of Maria Claudia Lutz, 43, Fernando Manrique, 44, their two autistic children, Elisa, 11, and Martin, 10, and the family dog, were found inside the house. They had died of carbon monoxide poisoning in a suspected murder-suicide.
Investigators found two gas cylinders outside the home, which was completely locked up when police arrived there on Monday.
They found a network of pipes running gas from the bottles through the ceiling, leading investigators to suspect the deaths were a deliberate act.
"There was a lot of pre-planning that went into this," a police source told the Daily Telegraph.
The incident has shocked friends of the family who had known Maria Lutz and Fernando Manrique as successful parents who cared well for their autistic children who had severe communication disabilities.
"The mum and dad were always in the garden and looking after the kids," neighbour Moiran Mayatt told the Sydney Morning Herald.
"[She] used to tell me how hard it was on her and her husband having two kids who were deaf and dumb," neighbour Sonja Perry told the Telegraph.
"They were... such a lovely, friendly couple. I'm shocked to see police cars outside their house. They never caused anyone problems."
Police are now working to establish where the gas was bought from.