The FBI arrested a 21-year-old Air National Guardsman in connection with the leak of highly classified documents including maps, intelligence updates and the assessment of Russia’s war in Ukraine.

Jack Teixeira, who works for the U.S. Air Force National Guard, was taken into custody Thursday afternoon without incident.

He will be charged with “unauthorized removal, retention and transmission of classified national defense information,” Attorney General Merrick Garland told reporters at a Washington news conference. “This investigation is ongoing. We will share more information at the appropriate time”

Garland said Teixeira will be arraigned in U.S. District Court in Boston. He didn’t say when and didn’t take questions.

The New York Times reported earlier Thursday that Teixeira was the leader of a gaming chat group where the classified documents first appeared.

The leak of dozens of pages of documents has been described as one of the most damaging and embarrassing intelligence disclosures in a decade. The documents were shared among a small group on the Discord text and video chat app before being picked up and circulated more broadly on Telegram messaging service, where international news organizations first became aware of them.

Earlier Thursday, President Joe Biden said the U.S. was close to concluding the investigation into the leak and downplayed its significance.

“There’s a full-blown investigation going on right now, as you know, with the intelligence community and the Justice Department,” Biden told reporters in Dublin on Thursday. Referring to who leaked the documents, Biden said, investigators were “getting close, but I don’t have an answer.”

“I’m not concerned about the leak,” Biden said. “I’m concerned that it happened. But there’s nothing contemporaneous” in the documents, he said.

The documents revealed U.S. assessments on the Russian invasion in Ukraine, including that Ukraine was dangerously close to running out of the missiles and interceptors needed to defend itself against the attacks. It also highlighted U.S. intelligence-gathering on allies including Egypt, South Korea and Israel.

The picture that has so far emerged of the leaker is of a military buff and gun enthusiast who started sharing the documents with online friends and acquaintances — some of them just teenagers — in an apparent bid to stave off isolation during the COVID-19 pandemic, according to a Washington Post profile published earlier Thursday.

The Pentagon and Justice Department launched investigations into the leak after the documents were discovered online and Teixeira is considered by intelligence and law enforcement officials to be a person of interest.

Investigators haven’t ruled out the possibility that a foreign adversary, like the Russian government, may have been involved in obtaining some of the classified documents, and potentially manipulating some of their contents.

Teixeira was mentioned on the Facebook page of the Massachusetts Air National Guard’s 102nd Intelligence Wing. One from July 2022 congratulated Teixeira after being promoted to Airman First Class. “Way to go!!!”

As part of the investigation, officials will seek to identify possible motives that Teixeira might have had if he is determined to be the leaker. Investigators will examine his comments in chats and whether there is any indication he sought to help another country.

The fact that there were classified markings on the documents makes it likely that the leaker knew he was committing some kind of harm, one official said.

The Justice Department’s investigation is being handled by its national security division, which deals with cases involving espionage, mishandling of classified information and nefarious actions by foreign governments. However, if it’s determined that the leak didn’t involve those issues, the case could be handled as a more routine criminal matter.

With assistance from Jack Gillum and Zoe Tillman.