The father of four children killed in the Margaret River shooting, which also claimed their mum and grandparents, has spoken about what he thinks happened.
The father of the four children killed in a suspected family murder-suicide has opened up on what led his father-in-law to pull the trigger, and revealed the suicide note that he left behind.
Aaron Cockman, who was estranged from the family, told Seven Network's Sunday Night program he believes Peter Miles killed his family as he had wanted to kill himself but did not want them to suffer.
Mr Miles, 61, his 58-year-old wife Cynda, their daughter Katrina, 35, and her four children - daughter Taye, 13, and sons Rylan, 12, Arye, 10, and Kadyn, eight - were found dead at Forever Dreaming Farm in Osmington, near Margaret River, on May 11.
Three guns licensed to Mr Miles were found at the hobby farm and the family all suffered gunshot wounds.
"The kids were so close to him, Peter, and Cynda," Mr Cockman said.
"It solves the problem. It solves his problem. How do I get rid of myself without everyone, all the kids suffering."
Mr Cockman also revealed the moment he found out his children were dead.
“My heart just dropped,” he said. “And I said, ‘Yeah, I think that’s my kids’. I said, ‘I’ve got the police coming here now.’ I still can’t believe that this is even happening."
Mr Cockman said the deaths came after a two-year custody dispute over the kids, which resulted in court orders, including over where the kids should live.
If those orders - which the program said it could not detail because of restrictions on reporting Family Court matters - had been followed, Mr Cockman said he thought his kids would still be alive.
"Yes. Definitely," Mr Cockman told the program.
The father told Sunday Night he believed the costly and lengthy custody dispute helped push Mr Miles over the edge.
He now wants to push for quicker decisions and an easier way for some court orders to be monitored and enforced, the program said.
"Out of this situation, if I can make things change ... It's better for every... for the kids," Mr Cockman said.
"It's better for dads, mums. And I'm going to put all my effort into that. I've got nothing else now."
During the interview, Mr Cockman also said Mr Miles, whom he had believed was dangerous, left a signed note inside a shed on the property where his ex-wife and children were killed, leaving the "house content" to him.
"Ex-husband, Aaron Cockman to have house content. Peter Miles," the note said.
Detectives and forensic officers spent days scouring the 11-hectare property, about 20km from the tourist hub of Margret River after the bodies were found.
The investigation into what led to the alleged multiple murders and suicide is continuing, and the coroner will eventually hold an inquest.
Readers seeking support and information about suicide prevention can contact Lifeline on 13 11 14.