Jack Teixeira, a Massachusetts Air National Guard member who pleaded guilty last year to leaking highly classified military documents about the war in Ukraine online, is scheduled to begin his court-martial on additional charges Monday.

Teixeira pleaded guilty last March to six counts of willful retention and transmission of national defense information under the Espionage Act, following his arrest in the most consequential national security breach in years. In November, he was sentenced to 15 years in prison in what then-Attorney General Merrick Garland said was a punishment that “demonstrates the seriousness of the obligation to protect our country’s secrets and the safety of the American people.”

In his court-martial, Teixeira faces charges of disobeying orders and obstructing justice. At a hearing last year, military prosecutors said a court-martial is appropriate given that obeying orders is the “absolute core” of the military. Teixeira’s lawyers argued that further action would amount to prosecuting him twice for the same offense.

Afterward, Teixeira hugged one of his attorneys, looked toward his family and smiled before being led from court. His family left without commenting to reporters, but his mother and others submitted letters to the court seeking leniency.

″I know Jack deeply regrets his actions and is ready to accept his punishment for his part in this situation,” his mother, Dawn Dufault, wrote. “While I understand the severity of his charges and the importance of ensuring justice, I implore you, Your Honor, to consider Jack’s true nature and his unique challenges, as I have observed over the years.”

The security breach raised alarm over the country’s ability to protect its most closely guarded secrets and forced the Biden administration to scramble to try to contain the diplomatic and military fallout. The leaks also embarrassed the Pentagon, which tightened controls to safeguard classified information and disciplined members found to have intentionally failed to take required action about Teixeira’s suspicious behavior.

Former FBI Director Chris Wray said in November that “Teixeira’s criminal conduct placed our nation, our troops, and our allies at great risk.”

Acting U.S. Attorney Joshua S. Levy addresses the media after the sentencing of Massachusetts Air National Guard member Jack Teixeira. (Pat Greenhouse/The Boston Globe via Getty Images)

“The FBI will continue to work diligently with our partners to protect classified information and ensure that those who turn their backs on their country face justice,” Wray said. 

Teixeira, of North Dighton, Massachusetts, was part of the 102nd Intelligence Wing at Otis Air National Guard Base in Massachusetts. He worked as a cyber transport systems specialist, which is essentially an information technology specialist responsible for military communications networks. He remains in the Air National Guard in an unpaid status, an Air Force official told the Associated Press. 

Authorities said he first typed out classified documents he accessed and then began sharing photographs of files that bore SECRET and TOP SECRET markings.

Prosecutors also said Teixeira tried to cover his tracks before his April 2022 arrest. Authorities found a smashed tablet, laptop and an Xbox gaming console in a dumpster at his house.

The Associated Press contributed to this report.