A second note found at the property of a family who died by murder-suicide in Perth on Friday is alleged to be a letter explaining the reasoning behind the deaths of the Clune family.

The bodies of father Jarrod Clune, mother Maiwenna Goasdoue and their two teenage sons Leon and Otis were found at the Mott Close property on Friday morning, in an apparent double murder-suicide.

Police said the alarm was first raised by a carer who went to the house just after 8am for a scheduled appointment, allegedly finding a note on the front door warning them not to enter and phone police.

When officers entered, they found the bodies of the parents at the rear of the property and the two teenage boys in another part of the house.

Two dogs and a cat were also found deceased.

While the first note found by police is alleged to be brief and a warning, this masthead understands a second note inside the property was structured as a “letter” that allowed police to make the determination the case was likely a double-murder suicide.

Police at the scene in Mosman Park on Friday morning.© 9News Perth

It is understood the second note contained details indicating a level of planning behind the act – going so far as to detail how the family wished their finances to be arranged following their deaths.

It is alleged to contain details regarding the mindset of the family prior to their deaths, and appeared to show the parents jointly decided to end their lives.

Family and friends have previously characterised Jarrod and Maiwenna as desperate for help, and said they experienced significant overwhelm while caring for their two boys, who both lived with autism.

One of the boys is believed to have experienced more challenges with his neurodevelopmental disorder than his brother.

Those close to the case said the family were at a desperate place before their deaths, with both parents attempting to cope as best as possible.

Some friends said the family did not receive enough support from government agencies and disability support providers.

Detective Sergeant Jessica Securo told the media on Friday the family had accessed care providers in the past.

However it is understood both Jarrod and Maiwenna were both primary carers of the boys, and were under significant pressure and suffering from exhaustion at the time of their deaths.

West Australian police confirmed the existence of the second note, but said they would not be providing details about what it said.

WA Police Detective Inspector Jessica Securo.© Hannah Murrphy

Securo said the ongoing investigation would attempt to determine when the family were last seen alive and how they died.

She confirmed there was no indication their deaths were violent.

Autism Association of WA chief executive Joan McKenna Kerr AM said there were resources available for anyone who may be struggling in the light of the news.

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

“We mourn the life of these two young people and their parents. Our heart goes 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.“

The Autism Association of WA said anyone struggling could call 9489 8900 for help.