Jack Teixeira -- a 21-year-old Air National Guard IT specialist -- allegedly orchestrated the most damaging leak of US classified documents in a decade, posting a trove of highly sensitive information in an online chat forum.

The documents, which soon spread across the internet, pointed to US concern over Ukraine's military capacity against invading Russian forces and showed Washington had apparently spied on allies Israel and South Korea, among other sensitive details.

Teixeira was brought in for the hearing -- which was attended by his father and others -- wearing handcuffs and dressed in an orange jumpsuit.

The "evidence supports detention," Magistrate Judge David Hennessy said, noting that "foreign countries know he was disloyal to the United States," and that the defendant "wasn't concerned about anyone else."

Prosecutors had argued that Teixeira might still have access to classified documents and that "hostile" nations could aid his escape if he was released from prison, also saying he had a history of making "violent" statements.

Teixeira wrote on social media in November that he wanted to "kill a ton of people" because it would be "culling the weak minded," the prosecution wrote in a court document.

- Repeated warnings -

Prosecutors also said the airman sought advice from another user about what type of rifle would be easy to operate from the back of an SUV, and that he searched mass shootings online.

They added that Teixeira owned "a virtual arsenal of weapons, including bolt-action rifles, rifles, AR and AK-style weapons, and a bazooka," with some of the firearms "just feet from his bed."

Teixeira's defense team said their client no longer had access to classified material and that the government was exaggerating the threat he posed, arguing he should be released into his father's custody pending trial.

The airman was arrested last month following a week-long probe and charged with two counts that carry maximum prison sentences of 10 years and five years.

Prosecutors also filed three partially redacted US Air Force memoranda -- dated between September 2022 and February 2023 -- this week that showed Teixeira received repeated warnings for misusing his access to classified information.

He was warned for taking notes on classified information, later potentially ignored a directive to stop "deep diving into intelligence information," and then was seen "viewing content that was not related to his primary duty and was related to the intelligence field," the documents say.

Despite the multiple warnings, Teixeira still held a top secret security clearance at the time of his arrest, according to an FBI affidavit.

Teixeira is accused of the "unauthorized retention and transmission of national defense information" and the "unauthorized removal and retention of classified documents or material."