Jack Teixeira, the US airman suspected of leaking hundreds of classified documents online, appeared for the first time in a Boston court on Friday.

The alleged leaker faced formal charges of unauthorized removal, retention, and transmission of classified national defense information.

Teixeira, an enlisted airman first class and member of the 102nd Intelligence Wing based in Cape Cod, Massachusetts, was arrested at his home by the FBI on Thursday.

The leaked Pentagon documents had been circulating online for weeks already before drawing the attention of the media – and of the US government – last week. The documents, which were color-printed and then photographed, ended up being uploaded to a gaming chat server.

A significant part of the trove of documents are related to the US and NATO war-planning effort in Ukraine, and included data on arms deliveries, training schedules, and estimates of losses sustained by both Moscow and Kiev, among other information.