"Police do not believe any other person is involved in these crimes".
"I will confirm all seven deceased suffered gunshot wounds", said Western Australia state Police Commissioner Chris Dawson in a media briefing Saturday.
Detectives are expected to spend several days at the property.
Investigators have not revealed the motive behind the shootings, with Mr Cockman only saying he previously enjoyed a close relationship with Ms Miles' parents.
Mr Cockman - who was estranged from Katrina - said he had not spoken to Peter and Cynda "since they cut him off from the kids".
Details have since emerged that Peter had recently been looking for work.
The bodies of their mother Katrina Miles, 35, and grandparents Peter Miles, 61 and his wife Cynda.
"[He was] just not someone who I would have thought was keen to find a new client or customer", he told Seven News Perth.
"You can't imagine what they're going through, you can only offer support, all you can do is express your sorrow and I expect the grieving process will go on for many years for that family", he said, reported ABC.
'How the hell Peter did that I still can't figure out, but if someone did it ... he did a good job, he did a really good job'.
"I wanted someone nearby to check my property twice a week, or so".
"This devastating tragedy will no doubt have a lasting impact on the families concerned, the whole community and, in particular, the local communities in our South West", he told reporters.
The farm is located in Osmington, northeast of Margaret River. Also, police do not conduct searches of the suspects, because there is a suspicion that the killer was one of those killed was a suicide.
"They will be supported by other specialist police units".
Speaking with locals today, many are battling to comprehend how something so savage could unfold on the sleepy rural property in Osmington, and how Margaret River has become the new home of a mass homicide - the biggest in Australia since the Port Arthur massacre.
The bodies of two adults were found outside near a shed that had been converted into living quarters - while the children and a third adult were discovered inside.
"This incident has shocked our local community to the core", said Pam Townshend, president of Augusta-Margaret River Shire, the district that includes Osmington, where the shooting occurred.
"The anger towards them now, is completely gone, I don't feel angry, I feel tremendous sadness for my kids, but I don't want anyone to feel anger".
"Cynda was a well-loved and very active member of our community. she had a deep commitment to the environment and she will be so sadly missed".