A young member of the Massachusetts Air National Guard was arrested by the FBI on Thursday afternoon in the investigation into leaks of classified military intelligence that started with a small online group and eventually led to hundreds of government secrets spilling out to the wider world.

The arrest came hours after people familiar with the case, who like others interviewed spoke on the condition of anonymity to discuss a developing investigation, identified the individual, 21-year-old Jack Teixeira, as the primary focus of the investigation. The Washington Post reported Wednesday that the individual who leaked the information shared documents with a small circle of online friends on the Discord chat platform, which is popular with gamers. In that group, a user said, Teixeira’s handles included jackthedripper.

Heavily armed FBI agents led Teixeira out of a family residence in Dighton, Mass., on Thursday afternoon. Wearing red gym shorts and a T-shirt, the young man was led into a waiting car. He could make an initial court appearance Friday in a case that has transfixed much of official Washington for the past week.

A friend of Teixeira described his motives to The Post as wanting to share – and show off – the secrets he knew to a small circle of online friends who bonded over video games. If convicted, Teixeira could end up serving years in prison.

In brief remarks to reporters at Justice Department headquarters, Attorney General Merrick Garland said Teixeira was arrested “without incident” in the “alleged unauthorized removal, retention and transmission of classified national defense information.” Garland did not take questions.

Teixeira served in a junior position, but he had access to an internal Defense Department computer network for top-secret information, called the Joint Worldwide Intelligence Communications System, according to a U.S. official familiar with the matter. That access would have allowed him the ability to read and potentially to print documents classified at the same level as many of the leaked files.

Teixeira told members of the Discord group Thug Shaker Central that he worked as a technology support staffer for the Massachusetts Air National Guard and at a base on Cape Cod, and this was how he was able to access classified documents, one member of the Discord server told The Post. Members of the group had come together initially because of their shared interest in guns and military gear, the member told The Post.

A Facebook post from the 102nd Intelligence Wing, with headquarters at Otis Air National Guard Base on Cape Cod, congratulated an individual by the same name for his promotion to airman first class in July.

The fast-moving investigation kicked off in early April when Pentagon officials first became aware that documents about an extraordinary range of subjects exposed how the United States spies on friends and foes alike. The leak of dozens of pages also upset senior Ukrainian officials, who had sought to keep details of their military’s vulnerabilities hidden as Russia’s war with Ukraine grinds on in its second year. The Post also reviewed approximately 300 photos of classified documents, most of which have not been made public.

Investigators are likely to probe how Teixeira, from his position as a technology support staffer at a base in Massachusetts, would have had access to highly classified information, some of which was used to brief senior leaders at the Pentagon. National Guard units perform some support services for active-duty units, including intelligence support for senior military officials, one U.S. official said. In that case, Teixeira could have had access to the kinds of highly classified documents that he is alleged to have shared with his fellow members on the Discord server, the official said.

In a written statement, the FBI said it was conducting “authorized law enforcement activity at the residence” where it arrested Teixeira. “Since late last week the FBI has aggressively pursued investigative leads, and today’s arrest exemplifies our continued commitment to identifying, pursuing, and holding accountable those who betray our country’s trust and put our national security at risk,” the FBI said.

Calls to Teixeira’s family were not immediately returned. Teixeira’s name was first reported by the New York Times.

President Biden, speaking in Ireland on Thursday, downplayed the significance of the compromised material. “I’m concerned that it happened, but there’s nothing contemporaneous that I’m aware of that is of great consequence,” Biden said.

Though not as massive as some previous leaks of highly classified material, the disclosure was nonetheless extraordinary because of the files’ recency: Some documents were just days old when posted earlier this year on Discord. The files gained wide notice when they began appearing on the social media platforms Telegram and Twitter last week. That meant the public – including Russia’s war planners – had access to sensitive intelligence assessments on Ukraine’s battlefield readiness prepared in late February and early March for top Pentagon officials such as Gen. Mark A. Milley, chairman of the Joint Chiefs of Staff.

The leaks have produced remarkable insights into U.S. intelligence activities worldwide, but their revelations about the war in Ukraine have proved particularly illuminating. Some of the material describes weaknesses in Ukraine’s air defenses and outlines its lack of ammunition while exposing considerable deficiencies within the Russian military, too. Many of the assessments date to February and March.

Brig. Gen. Patrick S. Ryder, a Pentagon spokesman, declined to comment on Teixeira’s emergence as the principal suspect in the leak investigation, referring questions to the Justice Department.

Speaking to reporters at the Pentagon, he said the Defense Department was “working around-the-clock” to assess the impact of the leaks and was taking steps to tighten access to classified information, including by updating distribution lists and reviewing which personnel required what kind of sensitive material.

He stressed that “stringent” rules were already in place, suggesting that no matter how tight the rules were on paper, they could be flouted by an individual determined to divulge intelligence.

“This was a deliberate criminal act, a violation of those guidelines,” he said. “To put it frankly, we’re continuing to conduct our operations and provide people with the information they need without missing a beat.”

Asked why a junior member of the National Guard would have access to briefings prepared for the military’s highest levels, Ryder declined to address Teixeira specifically but said that the military had always entrusted significant responsibility to young people who receive training and guidance.

“Think about a young combat platoon sergeant, and the responsibility and trust that we put into those individuals to lead troops into combat,” he said. “It’s called military discipline. In certain cases, especially when it comes to sensitive information, it also is about the law.”

The Discord leaks are damaging for what they reveal about the methods the United States uses to gather foreign intelligence, not just on Russia’s military and spy agencies but also on partners like Ukraine and Israel, as well as key allies in Asia, such as South Korea. The documents indicate where information and insights were gleaned by “signals intelligence” or “sigint,” essentially wiretapping or eavesdropping on calls or hacking into emails.

In one instance, the files reveal the use of an advanced satellite system that allows for high-resolution imaging of objects on the ground, one of the more closely guarded U.S. intelligence capabilities, and which could now be more susceptible to Russian jamming. In some cases, markings indicate that information was obtained at least in part by human means – perhaps spies.

A day after the Pentagon acknowledged it was probing the leaks, the Justice Department announced it had opened an investigation. Over the weekend, the Pentagon announced an “interagency effort” had been started to assess the impact of the leaks on national security. Officials across the U.S. government worked to determine the scope and significance of the disclosures, and contain diplomatic fallout. State Department officials said they were engaging with allies and partners to reassure them of the U.S. commitment to safeguarding intelligence.

Much of the information is tactical, a snapshot in time, and so its value “ages off” or diminishes over time, former intelligence officials noted, speaking on the condition of anonymity to discuss a sensitive matter. But that doesn’t mean there is no damage to sources and methods, especially in the near term, they said. And in the meantime, Russia can take advantage of what it learns to adjust its own war plans, they said.

(c) 2023, The Washington Post · Shane Harris, Samuel Oakford, Devlin Barrett, Perry Stein