WA Premier Roger Cook has described the Mosman Park double murder-suicide, which saw two teenagers killed by their parents, as an “unimaginable tragedy”.

Homicide detectives remained at the Mott Close property on Saturday, more than 24 hours after a family of four, and their three pets, were all found dead.

The Clune family — dad Jarrod, 50, mum Maiwenna, 49, and their two sons, Leon, 16 and Otis, 14 — were discovered by police after they were called to the home about 8.15am on Friday.

Police said a person, believed to have been scheduled to provide care for the two teenagers, called triple-0 after arriving at the home that morning.

Both boys lived with autism and were reportedly non-verbal, according to a neighbour who wished to remain anonymous.

The Sunday Times understands that a note found on the front door warned nobody to enter the house, but to call the police.

As the police investigation into how the boys died before their parents took their own lives continues, Premier Roger Cook urged anyone struggling following the incident to seek help.

“This is an unimaginable tragedy that will ripple throughout the community and the entire state,” he said in a statement.

“That the lives of two innocent children have been taken is heartbreaking.

“I urge anyone who is struggling to seek help.

“I want to offer my deepest condolences to all those affected and thank the first responders who attended what would have been an incredibly confronting scene.”

Autism Association of WA chief executive Joan McKenna Kerr said the incident had brought a “deep sense of grief”.

“We are deeply saddened by the news of this devastating tragedy,” she said.

“We mourn the lives of these two young people and their parents.

“Our hearts go out to all those who knew and loved them.

“We recognise that for many autistic people and their families, this news does not just bring sadness, but a deep sense of grief.

“If any family, or someone you know, is having difficulty with the news of this unimaginable tragedy, we urge you to reach out for professional support.

“You can also reach out to one of our Autism Advisors who will assist you to make connection with the support you need on (08) 9489 8900.”

Mott Close remained closed to the public on Saturday morning, with forensics and detectives observed coming and going from the home.

Police said all of the deaths, including two dogs and a cat found also deceased in the property, were not being treated as violent.