Father of kids killed in Australian massacre speaks out

The father of four children killed in a shooting massacre in Western Australia says he still loves the man believed to be responsible.

Aaron Cockman's former partner Katrina Miles, their 13-year-old daughter Taye and sons Rylan, 12, Arye, 10, and Kadyn, 8 were all found dead at a private property in Osmington on Friday (local time).

It's believed that the owner of the property Peter Miles - Mr Cockman's father-in-law and his children's grandfather - is responsible for their deaths.

Mr Miles and his wife Cynda were also found dead at the property. Three firearms belonging to Mr Miles were found at the scene.

Speaking to media for the first time since the tragedy, Mr Cockman said he wasn't angry at his father-in-law for the deaths of his children and former partner.

"I still love who Peter was," he said.

"If it wasn't for him, I wouldn't have Katrina, I wouldn't have her kids. So it's not some random guy off the street who's taken them away from me - he gave them to me and now he's taken them away.

"If it had to happen, there is no better person than that."

Mr Cockman was estranged from the late Ms Miles. He said he hadn't spoken to his parents-in-law "since they cut me off from my kids".

"Anger will destroy you," he said. "I'm sad, but I'll get through this."

Police are treating the massacre as a murder-suicide, and the investigation into why and how seven family members were killed is expected to take some time.

It's Australia's deadliest mass shooting since 35 people were killed in Port Arthur, Tasmania in 1996.