Tributes have begun to flow for the family.

Mother Maria Claudia Lutz, 43, was found in one room with one of her children and her other child was found alone in a separate room.

Fernando Manrique’s body was found in another room in the house.

Mr Manrique was spotted working on the roof of the house using power tools just days before the tragedy occurred. It is believed he was installing some sort of system to disperse the poison throughout the house.

Police have not yet found a note.

“There was a lot of pre-planning that went into this,’’ a police source said.

Maria Claudia Lutz and children Martin and Elisa. Picture: FacebookSource:Facebook

A neighbour said she watched Mr Manrique, 44, working on the house with power tools just two days before his death.

According to the Drake Business Logistics website, where Mr Manrique worked, his duties included being “actively involved in re-engineering and company mergers, where he has used his expertise and engineering training to successfully bring operational and strategic goals together”.

Ofik Thomassian, 72, lives directly across the street from where the family died.

“He was very friendly and she was very protective of those children,” Ms Thomassian said.

“She would lead them one at a time into the car, lock the door, and return to the house for the next child.”

Police are now attempting to locate where the gas was purchased.

Fernando Manrique and Maria Claudia Lutz with their children. Picture: FacebookSource:Facebook

The family’s pet dog was also found dead in the Davidson house. Picture: FacebookSource:Facebook

Tributes began to flow as neighbours mourned the loss of the loving family of four, including the couple’s two autistic children Martin, 10, and Eliza, 11.

Their family dog was also found dead nearby.

One by one, heartbroken friends laid flowers outside the home and shed tears for “the innocent children” whose lives were stolen far too soon.

Brooke Topschij (right) and locals drop flowers at the scene in Davidson where a family of four were found dead. Picture: John GraingerSource:News Corp Australia

Flowers are being placed by locals outside the Davidson house where the family was found dead. Picture: John GraingerSource:News Corp Australia

Locals are still in disbelief about what occurred in the quiet street. Picture: John GraingerSource:News Corp Australia

Neighbour Brooke Topschij was planning to celebrate her 18th birthday today but what was to be a joyous night out alongside friends has turned into a painful test of her strength.

The teenager has called on police not to delay releasing an official verdict on the deaths in order to give those who knew the family closure.

“It breaks my heart to think of how much pain the family was going through,” she said.

“We just want to know for sure if what we all think happened is what happened.

“It will give us peace of mind to know that it was not a murder, but a decision.”

Neighbour said Fernando Manrique was busy working on his home in the days before the incident. Picture: John GraingerSource:News Corp Australia

Police remained at the scene overnight and today.Source:News Corp Australia

Early investigations indicate the deaths were a result of murder-suicide. Picture: John GraingerSource:News Corp Australia

Ms Topschij was accompanied by another neighbour as she placed flowers and a private note on the doorstep of the family home.

“She looked after them but I have to say she never looked happy.

“She always had a very serious look on her face. Thinking back now, she looked like she was in pain. She probably had been for a very long time.”

Police remove one of the bodies from the Davidson property. Picture: Bill HearneSource:News Corp Australia

The bodies were believed to be found in separate locations. Picture: Bill HearneSource:News Corp Australia

Forensic crews combed the property last night. Picture: Bill HearneSource:News Corp Australia

Premier Mike Baird today expressed his shock over the tragedy.

“Like everyone across the state that sort of tragedy stops you in your tracks,” Mr Baird told a press conference today.

“I can’t imagine the circumstances but all I know - for their other family and friends - our hearts go out to them and our thoughts go out to them. Just tragic, tragic circumstances.”

Nearly 24 hours on from the discovery of the bodies, forensic crews are still working inside.

The property has been cordoned off and police are cautioning the well-meaning public from getting too close.

It could be weeks or even longer until the narrative leading up to the family’s death becomes complete.