Donald Day Jr, 58, was arrested in December by the FBI in Arizona on two counts of "interstate threats" 12 months after the fatal shootings at rural Wieambilla, west of Brisbane.
Day was later charged with illegally possessing firearms including three military-style rifles and a sawn-off pump-action shotgun along with a large cache of ammunition.
US prosecutors on Thursday were granted a protective order to provide Day's lawyer with evidence gathered by the Queensland Police Service's "ongoing investigation" into the shootings.
United States District of Arizona Judge John Tuchi said the order contained "reports or evidence provided by the Australian government to the FBI and reports of items of evidence seized".
"The discovery includes information relating to an ongoing investigation in Australia and includes personal identifiable information, communications with third parties, financial records and other sensitive information," Judge Tuchi stated.
The evidence is sealed by the court and further details cannot be disclosed to the public.
Day's lawyer has been ordered not to share the evidence with anyone except his client and other members of his defence team and must encrypt the material if they need to store it electronically or send it via email.
Constables Matthew Arnold and Rachel McCrow were shot in cold blood by Nathaniel, Gareth and Stacey Train after the officers arrived at the Wieambilla property.
Neighbour Alan Dare was also shot dead before the Trains were killed in a gunfight with specialist police later that night.
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.
Defence lawyer Jon Sands this month claimed prosecutors do not have sufficient evidence or legal precedents to support the interstate threat charges against Day, who has been denied bail.
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