US conspiracy theorist linked to Wieambilla shootings pleads guilty to watered-down charge

An American conspiracy theorist linked to the shocking Wieambilla shootings that left six people dead has pleaded guilty to a watered-down charge under a plea deal.

Arizona-based Donald Day Jr faced a United States court after a stockpile of weapons and ammunition were found at his rural property along with a sniper hide.

The convicted felon pleaded guilty to a single charge of unlawfully possessing firearms and ammunition as part of his plea deal that was signed off by an Arizona judge.

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He had also faced charges relating to making threats to public figures and FBI agents but they were dropped as part of the deal.

US prosecutors said Day - known online as "Geronimo's Bones" - corresponded via social media with Gareth and Stacey Train in Queensland around the time of the deadly Wieambilla ambush.

The couple, along with Nathaniel Train, murdered Queensland police officers Matthew Arnold and Rachel McCrow, along with neighbour Alan Dare in Wieambilla in 2022.

The Trains were killed in a shootout with police during an ensuing siege at their regional property.

Investigators established direct links between Day with Gareth and Stacey Train through posts from "Geronimo's Bones".

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Day described Queensland police as "malignant, malformed and malevolent", should be shown "absolutely no quarter", telling the Trains he wanted to be at Wieambilla in person.

Court documents detailed how Gareth and Stacey Train had posted an apocalyptic video on YouTube after the shootings, saying authorities "came to kill us and we killed them".'

"If you don't defend yourself against these devils and demons, you're a coward … we'll see you at home, Don. Love you," the Trains said.

Day was later found with a cache of nine high-powered firearms and hundreds of rounds of ammunition at a rural property in Heber, Arizona, that was equipped with a gun range and sniper hide, court documents showed.

"The firearms and ammunition were kept in the mobile home I shared with SS, in a room we called the 'gun room'," Day admitted in the plea deal.

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Day said he regularly accessed both the gun room and the weapons and also instructed others on how to use the firearms correctly.

According to court documents, Day had been prohibited from possessing weapons and firearms because of his violent criminal history.

Day faces a maximum penalty of up to 15 years in prison or a fine of $US250,000 ($A381,500) after pleading guilty to the single charge.

However, the plea deal for Day - who has served two years in custody - stipulates he will be sentenced under the low end of the sentencing guidelines.

Day is set to be sentenced on January 8.

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