The Guantanamo Bay prisoner who died over the weekend was well-known in legal circles.
The prisoner's lawyer identifies him as Adnan Latif, a 32-year-old from Yemen who has been held without charge at the U.S. base in Cuba since January 2002.
Attorney David Remes said Tuesday that Latif's family has been notified of his death. The U.S. military says he died Saturday and the cause is under investigation.
A judge had ordered Latfi's release in 2010, saying there was insufficient evidence to support allegations he attended an al-Qaida-linked training camp. A higher court overturned that order. And in June, the Supreme Court refused to hear Latif's appeal in a decision seen as a major setback to Guantanamo prisoners challenging their confinement.