Questions persisted, too, about the circumstances of Bergdahl's 2009 capture. Defense Secretary Chuck Hagel declined to comment on earlier reports that the sergeant had walked away from his unit, disillusioned with the war. Such matters "will be dealt with later," Hagel said.
But the former Pentagon official said it was "incontrovertible" that he walked away from his unit.
The military investigation was broader than a criminal inquiry, this official said, and it didn't formally accuse Bergdahl of desertion. In interviews, members of his unit portrayed him as a naive, "delusional" person who thought he could help the Afghan people by leaving his army post, the official said.
U.S. military and intelligence agencies had made every effort to monitor Bergdahl's location and his health, the official said, through both signals intelligence and a network of spies.
Nathan Bradley Bethea, who served as an officer in Bergdahl's unit, said in an article Monday on the Daily Beast website that Bergdahl was not on patrol, as some reports have suggested.
"There was no patrol that night," he wrote. "Bergdahl was relieved from guard duty, and instead of going to sleep, he fled the outpost on foot. He deserted. I've talked to members of Bergdahl's platoon_including the last Americans to see him before his capture. I've reviewed the relevant documents. That's what happened."
Hagel, visiting troops in Afghanistan, was met with silence when he told a group of them in a Bagram Air Field hangar: "This is a happy day. We got one of our own back."
At the White House on Monday, press secretary Jay Carney said the exchange "was absolutely the right thing to do." in much the same tone as the president over the weekend, he said: "The United States does not leave our men and women behind in conflict."
"In a situation like this, you have a prisoner of war, a uniformed military person that was detained," Carney said.
In weighing the swap, U.S. officials decided that it could help the effort to reach reconciliation with the Taliban, which the U.S. sees as key to more security in Afghanistan. But they acknowledged the risk that the deal would embolden insurgents.
Republicans pressed that point. "Have we just put a price on other U.S. soldiers?" asked Sen. Ted Cruz of Texas. "What does this tell terrorists, that if you capture a U.S. soldier, you can trade that soldier for five terrorists?"
Associated Press writers Darlene Superville in Washington, Rahim Faiez in Kabul, Afghanistan, Lolita C. Baldor at Bagram Air Field, Afghanistan and Zarar Khan in Islamabad contributed to this report.
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