Three firearms licensed to Peter Miles, who was found dead along with six others — including his four grandchildren — have been recovered at the crime scene, police said.
WA Police Commissioner Chris Dawson would not confirm if police believed the 61-year-old was the shooter, only saying the investigation at the scene would take several more days.
Police, who were called to the small community of Osmington early on Friday morning, found the bodies of seven people at the scene.
Katrina Miles and her four children were among the seven victims.
Ms Miles’ parents, Peter and Cynda Miles, were also killed in the incident.
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Police Commissioner Chris Dawson confirmed the firearms were licensed to Mr Miles.
WA Police have made a number of services available to the officers dealing with the incident.
The police chaplain has been supporting officers through what Commissioner Dawson described as one of the most confronting police have had to deal with.
It is the worst mass shooting in Australia since the Port Arthur massacre in 1996, in which 35 people were killed and another 23 seriously injured by lone gunman Martin Bryant.
The seven people killed in the murder-suicide include Katrina Miles and her four children. (Facebook: Katrina Miles)