A Guantanamo detainee who died Saturday was a former hunger striker who had recently been placed in a disciplinary cell after splashing a guard with a "cocktail"-- typically containing urine, a U.S. military official tells NBC News. 

The Naval Criminal Investigative Service is investigating the death of the detainee, whose identity and country of origin will not be released until his family is notified, said Navy Capt. Robert Durand, a spokesman for the U.S. detention facility.

But Durand provided some new details about the detainee's death -- the ninth to occur at Guantanamo since the prison opened in early 2002 and the first since an Afghan prisoner committed suicide in May of last year.

The detainee was found unconscious in his cell in Camp 5 on Saturday afternoon and was taken to the Naval hospital at Guantanamo where efforts to revive him failed. There were no cuts on his wrist or any other obvious signs of self-inflicted wounds, Durand said.

The detainee also had no serious medical problems. He had participated in a hunger strike last spring but ended it in June and was examined as recently as Aug. 22 when he was at 95 percent of his body weight, Durand said.

He had "fairly recently" thrown the "cocktail" at a prison guard, causing him to be placed in a solitary cell at Camp 5, said Durand. 

Although the death occurred on Saturday, military officials did not announce it until Monday in order to give officials time to notify the host country and family members of the detainee. That process has not yet been completed, but officials decided to release some details Monday because of concerns that some visitors to the base-- such as defense lawyers -- would learn about it anyway, Durand said. 

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The Miami Herald reported that a pathology and mortuary team was brought to the base on Sunday to attend to the body. A Muslim imam was summoned in order to give the man Islamic rites.

The dead man’s remains will be returned home after an autopsy, the Navy said.

The detention camp was set up to hold non-American captives suspected of involvement with al-Qaida, the Taliban or other Islamic militant groups after the September 11, 2001, attacks. Of the 779 men held there, 167 remain.

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Two of the earlier deaths were from natural causes and six were designated as suicides, most of them by hanging.

NBC News staff and Reuters also contributed to this report.

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