Asked if the two-minute emergency call made from the property at 5.15am on Friday was the reason police were so quickly able to rule out a gunman was on the loose, Mr Dawson said: "That's not for me to expand on now".
Mr Dawson said it was "not appropriate" to speculate on further details, but assured the community there were no "wider public safety issues".
JACQUELINE LYNCH: I spent much of my day talking to neighbours yesterday and as I said, they were very friendly and very warming and they said, I guess, the words they used to describe this incident was shocked and they were horrified.
Police have confirmed three long-arm firearms registered to Peter Miles were found at the scene of an alleged mass murder-suicide in Osmington.
Since the 1996 Port Arthur massacre, which left 35 dead and another 23 wounded in Tasmania, the country has only experienced one other so-called mass shooting - a man murdered his wife and three children before killing himself in 2014.
Peter Miles had a farm maintenance business and drew praise from clients for his work, while Cynda had also recently started a craft business that was developing a loyal following.
Police said they responded to an early-morning phone call and arrived to find a "horrific incident" in the small town of Osmington near the world-renowned wine-growing area south of Perth.
"I will confirm all seven deceased suffered gunshot wounds", he said. The bodies of two adults were located outside, five bodies were located inside a building on the rural property.
Katrina Miles and her children Take, 13, Rylan, 11, Arye, 10, and Kadyn, 8 were dead. That mass shooting prompted strict gun laws in the country, including penalties of up to 14 years in jail for unregistered firearms.
Police were attempting to make contact with the victims' relatives, Dawson said.
Australia has banned all semi-automatic rifles and all semi-automatic and pump-action shotguns, and has a restrictive system of licensing and ownership controls.
At one time, she used a Global Autism Project banner on her profile picture, which said the autistic community deserved more than just awareness.
"We are treating this as a matter in which clearly six persons are the subject of a homicide crime scene".
News.com.au has seen a social media post from someone who knew the family which said: "Lovely people, but insane ex-husband". He and Katrina apparently had been involved in an acrimonious split, leading Katrina to move in with her parents with her children.
Shire President Pamela Townshend said the seven deaths had a huge impact on the well-connected community.
Commissioner Dawson said the Margaret River community had banded together to help those affected.