Western Australia shooting could've been avoided, says father whose kids died

The Australian father who lost his family in the country's worst shooting in 22 years says the tragedy could have been prevented if a family court order hadn't been ignored.

Aaron Cockman's four children died in Margaret River at the hands of their grandfather on May 11.

He lost more in those pre-dawn minutes than many people do in their lives.

His children - Taye, Rylan, Arye, and Kadyn - were shot by Peter Miles, who also killed himself, his wife and his daughter.

Police have still not revealed a motive, but Mr Cockman told Channel 7 his father-in-law was depressed and suicidal.

"It solves the problem, it solves his problem - how do I get rid of myself without all the kids suffering?"

We may never know what drove Miles to murder, but Mr Cockman believes it could have been prevented if a family court order had been enforced.

He and his wife fought a custody battle, the details of which cannot be disclosed - but he says the family court order was ignored.

He says his children would "definitely" still be alive had it been enforced.

A suicide note has just been released, scrawled in childlike writing and signed 'Peter Miles'. It says only that Mr Cockman should have the house contents, but gives little insight into the man's mind.

Mr Miles gave his son-in-law all of his possessions, while taking away everything that Mr Cockman loved.