FBI agents arrested Massachusetts Air National Guardsman Jack Douglas Teixeira at a home in North Dighton, Massachusetts, Thursday in connection with a trove of classified documents that have been leaked online in recent months.
Attorney General Merrick Garland said Teixeira, 21, is being investigated for the "alleged unauthorized removal, retention and transmission of classified national defense information."
Teixeira, who joined the Air National Guard in September 2019, held the highest level security clearance granted by the federal government for top secret information, according to an internal Department of Defense email reviewed by Fox News.
His security clearance and access to classified government systems have since been revoked, according to another internal government document.
WHO IS JACK TEIXEIRA, THE AIR NATIONAL GUARDSMEN ALLEGEDLY BEHIND LEAKED CLASSIFIED DOCUMENTS?
Teixeira was most recently stationed at Otis Air National Guard Base as a member of the of 102nd Intelligence Wing. He was promoted to Airman 1st Class in July, according to the unit.
The FBI began surveilling Teixeira in connection with the leaks before Thursday but were forced to accelerate their plans to arrest him after The New York Times identified him on Thursday morning, a source briefed on the investigation told Fox News.
The New York Times report named Teixeira as the leader of a Discord group called "Thug Shaker Central" that consisted of roughly 20 to 30 young men.
Teixeira allegedly starting sharing classified documents with the private group in recent months, but the leaks gained wider attention after another member shared them in a public forum, according to the report.
Investigators don't believe the case ends with Teixeira and are looking at others who may be involved, a source told Fox News.
The National Guard said in a statement it is aware of the "alleged role a Massachusetts Air National Guardsman may have played in the recent leak of highly-classified documents" from the Pentagon.
PENTAGON DOCUMENT LEAK HAS IMMEDIATE IMPACT ON NATIONAL SECURITY: SUCKS UP ‘A LOT OF OXYGEN’
"The National Guard takes this issue very seriously and will support investigators," the National Guard said in a statement. "National security is our foremost priority, and any attempt to undermine it compromises our values and degrades trust among our members, the public, allies and partners."
Pentagon Press Secretary Brig. Gen. Pat Ryder called the leaks "a deliberate criminal act," saying that distribution lists for classified information are being reviewed.
LEAKER OF CLASSIFIED US INTELLIGENCE WORKS ON MILITARY BASE, POSTED THE DOCUMENTS ON DISCORD: REPORT
"We entrust our members with a lot of responsibility at a very early age," Ryder said at a press conference Thursday.
"You've received training, and you will receive an understanding of the rules and requirements that come along with those responsibilities. And you're expected to abide by those rules, regulations and responsibility. It's called military discipline. And, in certain cases, especially when it comes to sensitive information, it also is about the law."
Deputy Secretary of Defense Kathleen Hicks sent a memo to Pentagon officials Tuesday, warning employees against leaking classified information or downloading classified documents from unclassified sources.
"Do not access or download documents with classified markings from unclassified websites — either from home or work — as the data may be classified, it may be associated with hostile foreign elements, or it may contain malicious code or embedded capability that could introduce cyber threats into our information system," Hicks wrote in the memo obtained by Fox News.
Defense Secretary Lloyd Austin also ordered a review Thursday of "intelligence access, accountability and control procedures" to ensure that leaks like this don't happen again.
A large police presence was seen Thursday in Teixeira's quiet neighborhood in North Dighton, a small town about 35 miles south of Boston.
"This is where I live, so it's crazy to see all this going on here," a member of the community told Fox News Digital on Thursday.
"I don't know the parents, but I know of [Teixeira] because of my son. They rode the [school] bus together. They've lived there a long time and, obviously, as a parent, I feel horrible for them."
President Biden said earlier Thursday that the U.S. was "getting close" to finding the person responsible for leaking Pentagon documents that the Department of Defense has described as containing "sensitive and highly-classified material."
"I can’t right now [give an update]. There is a full-blown investigation going on with the intelligence community and Justice Department, and they are getting close," Biden told reporters during his trip to Ireland. "I don’t have an answer for you.
"I’m concerned that it happened, but there is nothing contemporaneous that I’m aware of that is of great consequence."
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The leaked documents mainly concern Russia's invasion of Ukraine but also include intelligence on China, the Middle East, Israel's spy agency Mossad and world leaders.
U.S. defense officials previously told Fox News the leak could be "bigger than Snowden" in terms of damage to intelligence and allied relationships.
Teixeira is expected to make his first court appearance Friday between 10 a.m. and 2 p.m., a source with the U.S. Attorney's Office for the District of Massachusetts said.
Fox News' Sarah Tobianski, Lorraine Taylor, and Rick Eggleston contributed to this report.