The remains of a U.S. serviceman from the Vietnam War were exhumed from the military's Tomb of the Unknowns at Arlington National Cemetery Thursday and removed for high-tech identification tests.

Private contractors, working carefully at night and under an unprecedented order by Defense Secretary William Cohen, used a diamond-tipped cutting tool to slice open thick granite slabs around the marble cover of the Vietnam War crypt at the tomb.Then a crane lifted the heavy cover and raised the casket out of the tomb, which is visited annually by tens of thousands of Americans and tourists from around the world.

After the private disinterment, the casket was draped with an American flag and the remains honored in a brief public ceremony before being taken in a hearse to Walter Reed Army Medical Center to begin DNA gene and other tests.

Cohen said at the ceremony the removal was done with "profound reluctance" but with a need to identify the nation's war dead.

The disinterment from the tomb, which also contains remains of U.S. military personnel killed in World War I, World War II and the Korean War, was conducted in response to a plea from the family of Air Force Lt. Michael Blassie, which believes his bones were buried there in 1984.

But Defense Department officials said the remains could have come from any of eight other U.S. troops lost in the area around the time that Blassie was shot down in South Vietnam May 11, 1972.

Bone fragments taken from the jungle were first tentatively identified as Blassie's, then changed to "unknown" based on tests taken before they were later buried in the tomb.

This time, the remains will be tested using modern DNA gene and bone technology in a process that could take up to three months or more.

"We disturbed this hallowed ground with profound reluctance," Cohen said at the brief ceremony at the tomb before the remains were removed to Walter Reed.

"We take this step only because of our abiding commitment to account for every warrior who fought and died to preserve the freedom that we cherish. If advances in technology can ease the lingering anguish of even one family, then our path is clear," he added.

Experts said a positive identification might not be possible, but that small pieces of bone will be tested using modern DNA skeletal technology.