British forces captured Ali Musa Daqduq in March 2007 in Basra. Daqduq was one of the last detainees the United States handed over to Iraq as American troops withdrew from the country in December 2011.
An Iraqi court has since ruled there is not enough evidence to continue holding Daqduq, though the United States "continues to believe that Daqduq should be held accountable for his crimes," said a U.S. State Department official, who spoke on condition of anonymity.
American military prosecutors said Daqduq is accused of murder, terrorism, espionage and other crimes, and is suspected of helping to organize a January 2007 raid in Karbala that killed five American soldiers, The New York Times reported Sunday.
Iraqi Prime Minister Nouri al-Maliki is under pressure from Iran to free Daqduq, observers say.
"It is a symbolic test for Maliki," said Ramzy Mardini, an adjunct fellow at the Iraq Institute for Strategic Studies in Beirut. "Is he more concerned about his relationship with Tehran or his relationship with Washington?"