Pentagon spokesman Ken Bacon said Cohen made the decision "after weighing the sanctity of the tomb with the need for the fullest possible accounting."
"If we can identify the remains now we have an obligation to try," he said. The families, he said, "deserve nothing less."
Remains of American servicemen from four wars are entombed in individual crypts at Arlington. Workers will be able to remove the casket containing the unknown veteran without disturbing other graves or marring the tomb.
A months-long CBS News investigation has determined the serviceman was most likely Michael Blassie, an air force pilot. In fact, CBS News Correspondent Eric Engberg and reporter Vince Gonzales have found evidence that senior officials had advance information they might be burying a "known" not an "unknown soldier."
Blassie's family praised the Secretary's decision. "I can't say we're surprised, but we're certainly pleased," Pat Blassie, the pilot's sister, said Thursday. "We're one step closer to bringing our family member home."
"We've been told that in a best-case scenario, we will have word in one month. And the worst-case scenario is that it will take 10 to 12 weeks," she said.
- The mystery began to be uncovered in 1983, when the Reagan Administration was pressing the military to find an unidentified American casualty of Vietnam who could be buried at the hallowed Tomb of the Unknowns.
The prime candidate - a set of partial remains - had sat for 11 years in an army center where army scientists struggled to identify the victim, then known only as X-26.
The military opened a far-reaching inquiry to see if X-26 could ever be buried as a soldier "known but to God."
- That's when Rogers Woolfolk - an army helicopter pilot who was an expert on aircraft equipment - was asked to do some detective work. Woolfolk's help was sought to look at remnants of a plane crash, to see what he could say about the pilot.
"We had things like a portion of a life raft, portion of a flight suit. There was part of a survival vest. There was a shoulder harness and a holster in there," Woolfolk recalled.
He was never told the equipment was found near the X-26 remains, which were soon to be interred at the tomb. Woolfolk also was not told that Blassie's I.D. card was found with the remains.
Sifting the equipment for clues, Woolfolk paid a lot of attention to the one-man life raft.
"The army didn't have anything flying with life rafts in them. And that led us to be looking at the Air Force," Woolfolk said.
- In the time period Woolfolk laid out, there had been only one A-37 crash where the body had not been recovered. The pilot of that plane was Michael Blassie.
oolfolk sent his findings - pointing to Blassie - to his superiors. But there is no record of Woolfolk's research in the army casualty center, or anywhere else.
Why his work, which would have warned officials the "unknown" candidate likely was known, was ignored is itself another unknown of a sad story
- Government scientists will use sophisticated mitochondrial DNA matching to determine blood type and whether there is any Blassie family genetic material. In theory, the remains could belong to eight other Air Force or Army fighter and helicopter pilots who went down in the An Loc area the same time as Blassie but whose bodies were never found, the Defense Department said.
Forensic evidence indicated the unknown Vietnam remains were of a man age 26-33, between 5-feet-5 1/2 and 5-feet-11 1/2 tall, and with type O negative blood. But Blassie, who was about 6 feet tall and age 24, had type A positive blood.
- Of the nine remains collected from the area around the same time, Capt. Rodney Strobridge, a 30-year-old Army helicopter pilot from Ohio, most closely matches the forensic evidence, according to Assistant Secretary of Defense of Reserve Affairs Charles Cragin. He was 5-feet-9 and 30 years old with type O negative blood. Strobridge crashed the same day as Blassie. But Cragin said other evidence found with the remains indicates they aren't from Strobridge, including an A-37 ejection seat, parachute and life raft gear his AH-1 Cobra helicopter didn't have.
The Pentagon has asked all nine families to give blood samples for use in DNA testing, but some have declined.
The actual testing of the remains will be performed at the Armed Forces DNA Identification Laboratory, outside Washington. The lab has already been able to help identify 72 sets of remains from the war using recently developed technology.
Should the tests establish that the remains are those of Blassie, the country will be faced with the question of whether to bury another Vietnam veteran in the Tomb of the Unknowns.
Several veterans groups have voiced opposition, citing scientific advances that make it impossible to declare any soldier truly "unknown" ever again.