An Army counterintelligence analyst who had been assigned to the Pentagon when it was attacked by terrorists died of an illness while serving in Iraq, his father said Wednesday.

Richard Eaton said military officials notified the family that his son, Staff Sgt. Richard S. Eaton Jr., died in his sleep Tuesday.

Maj. Bill Adams, a casualty assistance officer, said the cause of death remains under investigation but is thought to be pulmonary edema (search) -- a buildup of fluid in the lungs.

The family has few details about the death, the elder Eaton said, and they did not know whether he died from a strain of pneumonia that has killed other servicemen.

The elder Eaton, a spokesman for the University of New Haven (search), said his son's office in the Pentagon was struck by a hijacked jetliner during the Sept. 11, 2001, attacks. The father said the office was being remodeled at the time and the younger Eaton was in an office away from the Pentagon.

Eaton, 37, who was not married, was in the Army Reserves (search) and deployed to Iraq in March with the Fort Meade, Md.-based 323rd Military Intelligence Battalion, said his mother, Sharon Noble Eaton.

Earlier in his Army career, the younger Eaton had been offered a spot at the U.S. Military Academy in West Point, N.Y., but declined because he believed "real soldiering" was done in the field, his father said. In the years that followed he spent close to 10 years in Korea and had appointments in Honduras, Korea, Panama and El Salvador.

Eaton grew up in Guilford, on the Connecticut coast near New Haven.

He came from a long line of military men, including William Eaton, who helped reinstate the deposed leader of Tripoli and rescue American captives in the early 1800s. William Eaton's story is being made into a movie called "Tripoli" starring Russell Crowe.