THE family found dead in their home yesterday are believed to have been deliberately gassed to death with a poison that was released from numerous gas bottles found throughout the house.
Mother Maria Claudia Lutz, 43, was found in one room with one of her children and her other child found alone in a separate room.
Fernando Manriques' body was found in another room in the house.
Police have not as yet found a note, the Daily Telegraph reported.
"There was a lot of pre planning that went into this,'' said a police source.
A neighbour said she watched Mr Manriques working on the house with powertools just two days before his death.
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Police are treating the deaths of a family of four as a murder-suicide, as neighbours and friends say the Colombian parents struggled with their two autistic children.
The children Elisa, 11 and Martin, 10, were found dead in the home with their mother Maria Lutz, 43 and father Fernando Manrique, 44, on Monday after the school raised the alarm when the children and Ms Lutz failed to arrive.
Both of the children were deaf and autistic and described by the school as artistic.
When police visited the home in Davidson, in Sydney's north, they were confronted by the horrifying scene, which included the family's dead dog.
News Corp is reporting that none of the bodies showed signs of violence, and were found in separate locations in the house.
Autopsies and toxicology tests will determine the causes of death.
St Lucy's acting principal Warren Hopley said Ms Lutz was devoted to her children, but had sleepless nights coping with them.
"The school has been in a state of shock today and everyone will need some time to process what has happened," Mr Hopley told News Corp.
"Maria was someone who always was willing to help out no matter what the school was doing and today's events have had an impact everyone."
In April 2015 for Autism Awareness Day, Ms Lutz said it was a day to celebrate the lives of people with autism.
"My kids have (taught) me that giving small steps will take me to where I want to go and I will enjoy the journey even more."
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Man, woman, two children and dog found dead in home
A MAN, woman, and two children -- a boy and a girl, each with significant disabilities -- have been discovered dead in a New South Wales home.
Police went to the home in Davidson, on Sydney's north, at 11.20am after receiving reports regarding the welfare of those inside.
The two children found dead were a 10-year-old boy and a 11-year-old girl and each attended a nearby school for students with disabilities.
News Corp reports the family are thought to be Colombian, and moved to the area in 2005.
Police confirmed a "large dog" was also found dead at the home.
Fairfax is reporting the family found dead had lived in the area for "several years". The two children had autism, it reports.
It reported the 43-year-old wife was due to work in a local school canteen, and the alarm was raised when she didn't arrive.
There is no word yet on whether the dead were all from the same family.
Police said a crime scene has been established and "will be examined by forensic officers".
Superintendent Dave Darcy of the Northern Beaches Local Area Command said the family were not known to police.
He said it was a tragic and horrific incident.
"It's extremely confronting, the officers -- we consistently have these concern for welfare cases and unfortunately in some cases, this is what the police are confronted with.
"Two young children have died, two adults have died, I just want to keep this investigation … untainted so our investigators can clearly and concisely get the information they need to come to the truth of what's happened.
"The mother in particular is held in very high regard in the community.
"Since coming to Australia they've made a significant contribution to how we live, they've done a fantastic job."
Police were now seeking to make contact with the family's next of kin.
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