US federal investigators on Thursday arrested an individual in connection with last week's leak of classified US information on the war in Ukraine.

Attorney General Merrick Garland confirmed minutes later in a press conference that Jack T., a 21-year-old Air Force employee, was arrested after media outlets reported an arrest had been made in the case.

Garland said the arrest was made "in connection with an investigation into alleged unauthorized removal, retention and transmission of classified national defense information." He added federal agents took the suspect into custody "without incident." 

The FBI earlier said it made "an arrest and is continuing to conduct authorized law enforcement activity at a residence in North Dighton, Massachusetts." 

US media churned out information about the man earlier in the day, but there was no official confirmation about him being the individual believed to be behind the leaks.

The 21-year-old will make an initial appearance at the Federal District Court in Massachusetts.

Pentagon calls leak 'deliberate criminal act'

FBI agents converged at the suspect's Massachusetts home as heavily armed agents took a man wearing a T-shirt and shorts into custody outside the property. 

Pat Ryder, the Pentagon press secretary, said minutes before the arrest in a press conference that there was "an ongoing investigation."

"This was a deliberate criminal act," he added.

What did the classified documents reveal?

The classified documents ranged from briefing slides mapping out Ukrainian military positions to assessments of international support for Ukraine.

Some of the most sensitive information is purportedly related to Ukraine's military capabilities and shortcomings.

They also included other sensitive topics, including under what circumstances Russian President Vladimir Putin might use nuclear weapons.

But there are no clear answers as to how many documents were actually leaked. The Associated Press viewed approximately 50 documents, but some estimates put the total number in the hundreds.

The leak eventually led the Justice Department to open a criminal investigation into the disclosure of the documents.

President Joe Biden on Thursday told reporters in Dublin he was not overly concerned about the leak, saying there was "a full-blown investigation" underway.

What do we know about the suspect?

The suspect was an airman 1st class at Otis Air National Guard Base in Massachusetts, according to his service record. He joined the Air National Guard in 2019 and worked as a "Cyber Transport Systems Journeyman," or an IT specialist responsible for military communications networks, including their cabling and hubs. 

In that role, Jack T. would have had a higher level of security clearance because he would have also been given responsibility for ensuring protection of the networks, a defense official told The Associated Press, speaking on condition of anonymity.

US newspaper the Washington Post reported on Wednesday that the man suspected of leaking classified US documents was a "young, charismatic gun enthusiast." 

The publication cited fellow members of an online chat group on instant messaging platform Discord, with whom the man allegedly shared highly classified documents.

Jack T. supposedly oversaw the private chat group, whose members, mostly young men and teenagers, came together over a shared love of guns, racist online memes and video games, the New York Times reported.

Secret documents regularly posted on group chat

According to reports, group members said the man went by the name "OG" and would regularly post documents in the group. Among the documents posted were ones marked "NOFORN" which the Post reported was not meant to be shared with foreign nationals. 

The publication's report was based on interviews with two members of the group who spoke on condition of anonymity.

"When rendering hundreds of classified files by hand proved too tiresome, he began posting hundreds of photos of documents themselves," the Post reported.

Discord said in a statement that it was cooperating with law enforcement.

Editor's note: In line with German media privacy guidelines, DW has decided not to publish the suspect's full name and photo.

kb, rm/msh (Reuters, AFP)