Matthew Diaz, stationed from July 2004 to January 2005 at the US naval base at Guantanamo Bay, Cuba, faced a total of eight counts of three criminal charges and could spend thirtysix and half years in prison if convicted on all, the US Navy said.
Diaz, 40, was not charged with espionage and remains free, working at a Navy office in Jacksonville, Florida, ahead of a military hearing set for October in Norfolk, on whether the case will proceed to court-martial, Beth Baker, the regional Navy spokeswoman, said.
The charges relate to improper safeguarding of classified information and improper forwarding of classified information to a person not authorised to receive it.
Diaz was accused of mailing "a multi-page classified document that contained the names and other identifying information" about Guantanamo detainees from that base to "a non-governmental organisation not authorised to receive it", Baker said.
Baker declined to identify the organisation beyond saying it was in the United States, and said the group turned over the document to federal authorities, prompting the investigation that led to the charges.
As deputy staff judge advocate at Guantanamo, Diaz's job was to give legal advice on a variety of issues to military commanders, Baker said, and he never represented any Guantanamo detainees.
The charge sheet stated between December 20, 2004 and February 28, 2005, Diaz violated a Navy regulation by failing to properly safeguard and store classified secret information and failing to properly transport and mail such information by sending it via routine first-class mail. It also said he was derelict in his duties.
While the United States for more than four years refused to identify those held at Guantanamo, the Pentagon this spring released the names and nationalities of all the detainees it said had ever been held under military control there.
Diaz was formally charged on Monday, Baker said.
The Pentagon said the US military currently holds about 445 detainees at the Guantanamo facility, most held without charges for more than four years.
The United States has faced international criticism over the indefinite detention of Guantanamo detainees amid allegations of their mistreatment.