A Sydney family who were found dead in their home on Monday are believed to have been deliberately gassed with a poison that was dispersed throughout the house.
The alarm was raised on Monday after Colombian-born Maria Claudia Lutz, 43, didn't show up for her volunteering shift at special needs school St Lucy's, and her children weren't in class.
Police found Ms Lutz's body at around 11:20am that morning inside the family's home, alongside the body of her husband Fernando Manrique, 44, their children Elisa, 11, and Martin, 10, and the family dog.
It is believed a poison gas was released using devices around the house.
"There was a lot of pre-planning that went into this," a police source told The Daily Telegraph.
The whole community has been shaken by the sudden deaths.
"I used to walk up to the oval and they'd say hello," neighbour Sonja Perry told The Daily Telegraph.
"They were just a normal family, the kids would play in the front yard."
Ms Perry said sometimes Ms Lutz had found it difficult to cope with raising Elisa and Martin. It's understood both of the children had high complex special needs.
"[She] used to tell me how hard it was on her and her husband having two kids who were deaf and dumb," Ms Perry said.
"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 purchased from.