An American accused of messaging the Australian family who shot two police officers later used the killings to bolster his alleged threats against public figures, US prosecutors have said.
Donald Day Jr, 58, was arrested in December 2023 by the FBI in Arizona on two counts of "interstate threats" following the December 2022 fatal shootings in Queensland.
Constables Matthew Arnold and Rachel McCrow were gunned down in cold blood by Nathaniel, Gareth and Stacey Train after the officers arrived at a Wieambilla property west of Brisbane.
Neighbour Alan Dare was also shot dead before the Trains were killed in a gunfight with specialist police later that night.
Day's lawyer told Arizona's District Court in late December that the charges should be thrown out because Day was not accused of making statements of intent to harm any specific person.
Prosecutors on Wednesday provided the US government's response, urging the court not to dismiss the charges.
They argued that Day made "true threats" and used the Queensland shooting as an example of what he wanted to carry out himself.
Between May 2021 and December 2022, Day, of Heber, Arizona, is accused of repeatedly sending messages about a "Christian end-of-days ideology" known as premillennialism to the Trains.
Gareth and Stacey Train uploaded a video on a now-deleted YouTube account hours after the fatal shootings, referring to police as "devils and demons" and sending love to someone called Don.
On Wednesday, prosecutors said Day uploaded a video to YouTube four days later in which he said the Trains "have done exactly what they were supposed to do, and that is kill these f***ing devils".
Day allegedly went on to state "it is no different for us" and later threatened to kill the director-general of the World Health Organisation.
Day also allegedly made threats against law enforcement officers, referring to them as "the devils" and claiming he had many firearms.
Prosecutors said Day's videos were not "jests (or) hyperbole" or taken out of context.
Queensland Police and the FBI have said they are still investigating the alleged contact between the Trains and Day, who has been denied bail.
