Jack Teixeira, a member of the Massachusetts Air National Guard accused of leaking classified military documents on social media, pleaded guilty Monday to one of the worst national security breaches in recent years.

Jack Teixeira, who has been in custody since his arrest last April, pleaded guilty during a hearing in federal court in Boston after striking a plea deal with prosecutors who plan to ask a judge to sentence him to 16 years in prison, Reuters and report News.ro.

The 22-year-old pleaded guilty to six counts of possessing and knowingly transmitting classified national defense information after Teixeira allegedly shared a stack of classified files with a group of gamers on the Discord messaging app last year.

In exchange for the guilty plea, prosecutors agreed not to charge Teixeira with other violations of the Espionage Act or other crimes. He agreed to be sentenced to at least 11 years in prison, and prosecutors said they would recommend 16 years and eight months.

District Judge Indira Talwani set sentencing for September 27.

Prior to his arrest at his mother’s home in North Dayton, Massachusetts, Teixeira was stationed at Otis Air National Guard Base in Cape Cod, Massachusetts. He did not have a higher education, but worked as a cyber security technician. According to prosecutors, despite being a low-level employee, Teixeira received a top-secret clearance and, beginning in January 2022, began accessing hundreds of classified documents related to topics such as Russia’s invasion of Ukraine.

He did so despite his superiors warning him twice in 2022 that he was using classified information and warning him not to conduct “deep searches” in databases, he told Assistant US Attorney Jason Casey in court on Monday .

Using the username “TheExcaliburEffect,” Teixeira shared classified information on Discord, a private server-like chat room–while boasting that he had access to “stuff about Israel, Palestine, Syria, Iran, and China.”

The leaked documents contained top-secret information about allies and adversaries, starting with troop movements in Ukraine and ending with Israel’s Mossad intelligence agency.

In December, the US Air Force announced it had taken disciplinary action against 15 personnel following the leak and removed Col. Sean Riley from command of Teixeira’s unit. The Air Force Inspector General’s report on the incident found that some members of Teiseria’s unit and his leadership “had information about no fewer than four separate incidents of his questionable activity.” A smaller number had a more complete picture of his information-seeking behavior and “intentionally failed to report all the details of these security concerns/incidents,” the report said.