BOSTON (AP) — Jack Teixeira, the Massachusetts Air National Guard member accused of leaking highly classified military documents about Russia’s war in Ukraine and other national security secrets, is expected to plead guilty on Monday in federal court.

The 22-year-old is due to appear in Boston’s federal courthouse for a change of plea hearing nearly a year after he was arrested in the case stemming from the most consequential national security leak in years.

Teixeira, of North Dighton, Massachusetts, has been behind bars since his April arrest in the case that raised alarm over America’s ability to protect its most closely guarded secrets and forced the Biden administration to scramble to try to contain diplomatic and military fallout.

The leak led the Pentagon to tighten controls to safeguard classified information, and the Air Force disciplined 15 personnel as its inspector general found last year that multiple officials intentionally failed to take required action about Teixeira’s suspicious behavior.

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Teixeira had previously pleaded not guilty to six counts of willful retention and transmission of national defense information under the Espionage Act. Each count is punishable by up to 10 years in prison.

A judge last year ordered Teixeira to remain behind bars while he awaits trial after prosecutors revealed he had a history of violent rhetoric and warned that U.S. adversaries who might be interested in mining Teixeira for information could help him escape.

Teixeira remains in the Air National Guard in an unpaid status, the Air Force said.

Neither prosecutors nor defense attorneys have provided further details about Teixeira’s plea agreement. An attorney for Teixeira has not responded to messages seeking comment.

Teixeira was part of the 102nd Intelligence Wing at Otis Air National Guard Base in Massachusetts when authorities say he illegally collected military secrets and shared them with other users on Discord, a social media platform popular with people playing online games. Teixeira worked as a “cyber transport systems specialist,” essentially an IT specialist responsible for military communications networks.

Authorities said he first typed out classified documents he accessed and then began sharing photographs of files that bore SECRET and TOP SECRET markings. The leak exposed to the world unvarnished secret assessments of Russia’s war in Ukraine, the capabilities and geopolitical interests of other nations and other national security issues.

Prosecutors have said little about an alleged motive. But members of the Discord group described Teixeira as someone looking to show off, rather than being motivated by a desire to inform the public about U.S. military operations or to influence American policy.

Prosecutors have said Teixeira continued to leak government secrets even after he was warned by superiors about mishandling and improper viewing of classified information. In one instance, Teixeira was seen taking notes on intelligence information and putting them in his pocket.

The Air Force inspector general found that members “intentionally failed to report the full details” of Teixeira’s unauthorized intelligence-seeking because they thought security officials might overreact. For example, while Teixeira was confronted about the note, there was no follow up to ensure the note had been shredded and the incident was not reported to security officers.

It was not until a January 2023 incident that the appropriate security officials were notified, but even then security officials were not briefed on the full scope of the violations.

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Associated Press reporter Tara Copp in Washington contributed.