Speaking outside the Margaret River police station Cockman said he felt "tremendous sadness" over the death of his children.
Police were attempting to make contact with the victims' relatives, Mr Dawson said.
Katrina and her four children had been or were students at Margaret River Primary School.
A forensic investigation at the property is continuing. We are stunned and still trying to understand how this could happen.
"We are devastated by this shocking event".
"We respectfully ask that the community refrain from speculating on the circumstances surrounding this tragic incident".
In Osmington that in Western Australia, was discovered seven bodies, four of them children.
Police forensics investigate the death of seven people in a suspected murder-suicide in Osmington, east of Margaret River, south west of Perth, Australia Friday, May 11, 2018.
Mr Dawson said he would not release the triple zero call made about 5.15am on Friday, which he previously said was by a male connected to the property.
Aaron Cockman has seen firsthand the emotional anguish Peter Miles had gone through in recent years.
However the 61-year-old was looking for "vineyard and farm work" in the region as recently as Wednesday.
Police have revealed few details about the recent killings, and it is not clear whether there was more than one shooter.
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Mr Miles was found slumped in a chair on the back porch, with a self-inflicted gunshot wound.
He purchased the 30-acre farm in late 2014 alongside along with his spouse Cynda.
It was believed those who died lived at the property, about 10 minutes drive from Margaret River, a popular tourist destination renowned for its wine, surf and natural beauty.
Cynda Miles worked for a local community group, according to neighbours and public records.
Police confirmed three guns located at the scene were registered to Peter, and that he was a suspect in the murder of his wife, his daughter and his four grandchildren.
"I wanted someone nearby to check my property twice a week, or so".
Mr Dawson refused to disclose any additional particulars in regards to the man who tipped police off. He added that the police expected to be on the site for up to five days.
In a statement, the extended family said on Saturday they were devastated.
The family had all been shot by firearms licensed to grandfather Peter Miles, who was among the dead. "There was just a lot of love in that family".
"But this is not how I would want to get back at them".
"Margaret River is one of the more famous parts of Western Australia, and it's sad now outside our great state, and internationally, it will be associated with this tragedy".
"A female adult was found deceased inside the main house and a female adult and four children were found deceased in what I would describe as a converted shed structure".