Matthew Mark Diaz is a former active-duty Lieutenant Commander (LCDR) and Judge Advocate General's Corps (JAGC) officer in the United States Navy.

[1][2] In mid-to-late 2004, Diaz served a six-month tour of duty in Guantanamo Bay, Cuba as deputy director of the detention center's legal office.

After obtaining his Juris Doctor degree at Washburn University School of Law in 1994, Diaz was commissioned as a naval officer in the U.S. Navy's Judge Advocate General's Corps.

[12] Diaz served eight years as an enlisted man in the United States Army, prior to being commissioned in the USN's Judge Advocate General Corps, after earning a law degree.

On July 28, 2006, Diaz was formally charged with improperly mailing suspected classified information about detainees in the Guantanamo Bay detainment camps to an individual unauthorized to receive it, in this case the Center for Constitutional Rights.

[14] Scott Horton wrote: Matthew Diaz found himself in a precarious position—as a uniformed officer, he was bound to follow his command.

[15]Barbara Olshansky, of the Center for Constitutional Rights, was the recipient of the document, placed alongside an unmarked Valentines Day card.

[16][17] While Olshansky had requested a list of all detainees being held at Guantanamo Bay detainment camps, the military had failed to provide one.

Diaz was not directly involved in either the defense or prosecution of the ten detainees who faced charges before the Guantanamo military commissions.