The family opened fire when four police officers arrived on December 12 for a routine missing persons investigation at their home in the small town of Wieambilla in Queensland.
Three family members -- Gareth Train, his wife Stacey Train, and his brother Nathaniel Train -- killed two officers and one neighbour, before dying in a shootout with police.
Counter-terrorism and intelligence police have since searched for a motive for the bloody event, trawling through diaries, books, phone messages, emails, witness statements and body-worn camera footage, police said.
The investigation found that the three family members "acted as an autonomous cell and executed a religiously-motivated terrorist attack", said Queensland's deputy police commissioner, Tracy Linford.
The family subscribed to a fundamentalist belief known as "premillennialism", which predicted Christ would return to Earth after a period of tribulation, widespread destruction and suffering, she told reporters.
An examination of Stacey Train's diary in particular indicated that a range of things perpetuated their belief, such as Covid-19, climate change and global conflicts, Linford said.
Police were still conducting a "major investigation" for a Christian 'terrorist attack', she said, adding that there was no evidence anyone else was involved in the incident.
The deceased police officers were identified at the time as 26-year-old Rachel McCrow and 29-year-old Matthew Arnold. Both were constables.
The family subscribed to a fundamentalist belief known as “premillennialism”, which predicted Christ would return to Earth after a period of tribulation, widespread destruction and suffering, Linford told reporters.
An examination of Stacey Train’s diary in particular indicated that a range of things perpetuated their belief, such as Covid-19, climate change and global conflicts, Linford said.
The investigation found that the three family members “acted as an autonomous cell and executed a religiously motivated terrorist attack”, said Queensland’s deputy police commissioner, Tracy Linford.
According to BBC News, authorities said it was the first time Christian extremist ideology had been linked to a terror attack in the country.
“Christian extremist ideology has been linked to other attacks around the world, but this is the first time we’ve seen it appear in Australia,” Ms Linford said.