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.
Four children and three adults were found dead at a rural property near the Margaret River wine region in Western Australia yesterday (May 11) in an apparent murder-suicide.
The children's father, Aaron Cockman, is not being investigated by police despite a marriage breakup with his estranged wife.
He said when he recently learnt another of his sons was seriously ill with kidney problems, it tipped him over the edge. I feel tremendous sadness for my kids.
Mr McGowan said he had spoken to Mr Cockman, who was clearly grief stricken.
"He's thought this through, he's not snapped", he said. "I just feel sick to the stomach".
In 2016, 20 years after the shooting in Tasmania, The Post's Christopher Ingraham cited research published in the Journal of the American Medical Association showing that Australia had not had a mass shooting since the changes and that suicide rates in the country had been on the decline.
Police were called before dawn to a residence in the village of Osmington, some 13 miles northeast of Margaret River and 170 miles south of Perth.
Cynda Miles lived at the rural property where seven people were found dead.
Cockman said the last time he saw his children was when they watched the Avengers together two weekends ago.
Crime-scene and homicide detectives were called to investigate.
The neighbour's revelations came as the devastated family of the seven dead try to understand how it happened.
"They will be supported by other specialist police units".
Another resident, former shire councillor Felicity Haynes, described them as being well-known for their volunteer and charity work, particularly in the area of sustainability.
Police addressed the media in a press conference today.
The farm is located in Osmington, northeast of Margaret River.
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.
In an editorial a year ago, the Age said it respected citizens' rights but that there are "some freedoms that have no place in a civilised society, and none more so than the carrying of illegal firearms".
"Police are now responding to what I can only describe as a horrific incident", he said.
Recent US mass shootings to make global headlines include the deaths of 17 people at a Florida high school in February, 58 people on the Las Vegas Strip in October 2017 and 49 people at an Orlando gay nightclub in 2016.
"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".