The Air National Guardsman accused of posting a trove of classified documents to social media has been formally indicted on six counts of willful retention and transmission of classified information related to national defense, the Justice Department announced on Thursday.

Jack Teixeira, 21, was arrested and charged under the Espionage Act in April. He remains in federal custody.

Teixeira allegedly took classified information from Otis Air National Guard Base and posted it on social media.

"Teixeira also posted images of classified documents to the social media platform, which bore standard classification markings -- including 'SECRET,' 'TOP SECRET,' and SCI designations -- indicating that they contained highly classified United States government information," the Justice Department said in its announcement of the indictment.

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