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(CNN) - Former Army Sgt. Evan Buetow was the team leader with Bowe Bergdahl the night Bergdahl disappeared.
"Bergdahl is a deserter, and he's not a hero," says Buetow. "He needs to answer for what he did."
Within days of his disappearance, says Buetow, teams monitoring radio chatter and cell phone communications intercepted an alarming message: The American is in Yahya Khel (a village two miles away). He's looking for someone who speaks English so he can talk to the Taliban.
"I heard it straight from the interpreter's lips as he heard it over the radio," said Buetow. "There's a lot more to this story than a soldier walking away."
The Army will review the case of Sgt. Bowe Bergdahl "in a comprehensive, coordinated effort," Secretary of the Army John McHugh said Tuesday.
The review will include speaking with Bergdahl "to better learn from him the circumstances of his disappearance and captivity," he said.
The night Bergdahl disappeared, says Buetow, the platoon was at a small outpost, consisting of two bunkers and a perimeter of military trucks. Buetow was in one of the bunkers, and Bergdahl was supposed to be in a tent by one of the trucks.
Then a call came through on the radio.
"I'll never forget that line, 'Has anyone seen Bergdahl?'" says Buetow.
Firsthand accounts from soldiers in his platoon say Bergdahl disappeared while he was on guard duty.
Buetow says Bergdahl was about to go on guard duty, but when a fellow soldier went to wake him, he was not in his tent. He had left behind his weapons, his bullet-proof vest, and night vision gear.
"I immediately knew, I said, 'He walked away. He walked away,'" said Buetow.
Bergdahl walked off the observation post with nothing more than a compass, a knife, water, a digital camera and a diary, according to firsthand accounts from soldiers in his platoon.
Buetow was involved in the immediate search for Bergdahl, pushing a patrol into a nearby local village.
"Immediately as we left the base, two small boys walked up to us, and they told us that they saw an American crawling in the weeds by himself," said the former Army sergeant. The search followed that lead, and others, for months.
"For 60 days or more, I remember, just straight, all we did was search for Bergdahl," said Buetow, "essentially chasing a ghost because we never came up with anything."
At least six soldiers were killed in subsequent searches for him, according to soldiers involved in those operations.
The Pentagon was not able to provide details on specific operations in which any soldiers were killed during that time were involved.
Buetow says even though those operations were not "directed missions" to search for Bergdahl, there was an underlying premise of acting on intelligence to find the missing soldier.
"The fact of the matter is, when those soldiers were killed, they would not have been where they were at if Bergdahl hadn't left," says Buetow. "Bergdahl leaving changed the mission."
Many soldiers in Bergdahl's platoon said attacks seemed to increase against the United States in Paktika province in the days and weeks following his disappearance.
"Following his disappearance, IEDs started going off directly under the trucks. They were getting perfect hits every time. Their ambushes were very calculated, very methodical," said Buetow.
It was "very suspicious," says Buetow, noting that Bergdahl knew sensitive information about the movement of U.S. trucks, the weaponry on those trucks, and how soldiers would react to attacks.
"We were incredibly worried" that Bergdahl was giving up information, either under torture, or otherwise, says Buetow.
President Barack Obama said Tuesday that no matter what the circumstances of an American soldier's capture, the United States has a duty to get him or her back.
"It's great that he’s back and that we can have that very small victory, if you can even call it a victory. Because I believe what we gave up for that - we gave up a lot for what we got back," says Buetow.
For more of our interview with former Army Sgt. Evan Buetow, click here, or check out the video below.