Hassoun disappeared from his unit in Iraq's western desert in June 2004. The following month he turned up unharmed in Beirut, Lebanon and blamed his disappearance on Islamic extremist kidnappers. He was returned to Lejeune and was about to face the military equivalent of a grand jury hearing when he disappeared again.
Flanagan, said the Hassoun case is unrelated to the matter of Army Sgt. Bowe Bergdahl, who disappeared from his post in eastern Afghanistan in June 2009 under unexplained circumstances. Members of Bergdahl's unit have said he walked away on his own and should face desertion charges.
It is unclear where Hassoun, 34, has spent the past nine years after disappearing during a visit with relatives in West Jordan, Utah in December 2004. He was born in Lebanon and is a naturalized American citizen.
At the time of his disappearance from a Marine camp in Fallujah in western Iraq in June 2004 Hassoun was serving as an Arabic translator.
Seven days after his June 2004 disappearance, a photo of a blindfolded Hassoun with a sword poised above his head turned up on Al-Jazeera television. A group called the National Islamic Resistance/1920 Revolution Brigade claimed to be holding him captive.
On July 8, 2004, Hassoun contacted American officials in Beirut, Lebanon, claiming to have been kidnapped. After a Navy investigation, the military charged Hassoun with desertion, loss of government property, theft of a military firearm for allegedly leaving the Fallujah camp with a 9 mm service pistol, and theft of a Humvee.
In the initial months following his return to Camp Lejeune, Hassoun was not held in confinement because charges had not yet been brought against him. He was considered non-deployable until the case was resolved, but he was allowed to make personal trips.
A January 2005 hearing on the matter was canceled when Hassoun failed to return to Camp Lejeune from his Utah visit. His commanders then officially classified him as a deserter, authorizing civilian police to apprehend him.
In a February 2005 interview with the Associated Press in Salt Lake City, Hassoun's brother, Mohamad, said Wassef Ali Hassoun was a victim of anti-Muslim bias in the U.S. military. The Marine Corps denied this.
The brother also said the pressure of facing desertion charges was partly to blame for Hassoun's decision to flee while in Utah.
"Instead of them giving him medals and making him feel good about his service and what he was doing for his country, they gave him an Article 32," Hassoun said of the military court proceedings that his brother was to have faced in January 2005.
Family members have said they last saw him on Dec. 29, 2004.