GWEN IFILL: A sincere, if misguided, young soldier, or a deserter and even a traitor?

Bowe Bergdahl, the Army sergeant who walked off his post in June 2009, now faces court-martial on charges of desertion and endangering troops.

Still unclear, what motivated Bergdahl to leave his comrades.

The "PBS NewsHour" and The New York Times were recently provided with the transcript of Bergdahl's only interview with the Army's top investigating officer, in which the sergeant lays out what made him do it.

Jeffrey Brown has the exclusive details.

JEFFREY BROWN: May 31, 2014.

PRESIDENT BARACK OBAMA: This morning, I called Bob and Jani Bergdahl, and told them that, after nearly five years in captivity, their son Bowe is coming home.

JEFFREY BROWN: Army Sergeant Bowe Bergdahl's release came after the U.S. agreed to free five Taliban leaders being held at Guantanamo Bay. To some, the announcement brought joy and relief. But others, including soldiers who served in his unit, saw something different.

JOSH KORDER, Former U.S. Army Sergeant: It's very frustrating to me to see Bergdahl's family on the TV being shown to everyone. He's, at best, a deserter and, at worst, a traitor.

JEFFREY BROWN: Five years earlier, Bergdahl had served at a remote outpost called Mest Malak in Southeastern Afghanistan. This is one of the post's observation points on the top of a hill.

And these are the last known pictures of Bergdahl in the days before he walked off the post. He was captured by the Taliban the day after he left.

SGT. BOWE BERGDAHL, U.S. Army: All's I was seeing was basically leadership failure.

JEFFREY BROWN: Bergdahl had told the podcast "Serial" that leadership problems were endangering his unit, and that he planned to hike to another post to alert a senior Army commander.

SGT. BOWE BERGDAHL: I was fully confident that when somebody actually took a look at the situation, and when people started investigating the situation, that people would understand that I was right.

JEFFREY BROWN: Now there's more insight into Bergdahl's thinking. It comes in a transcript provided exclusively to the "NewsHour" and The New York Times by his attorney from an interview Bergdahl gave two months after his release to the Army's senior investigating officer.

In it, he speaks of concerns he had with immediate commanders from the very beginning of his enlistment.

Here, for example, in a passage read by a "NewsHour" producer, he described a platoon inspection before his deployment to Afghanistan.

PRODUCER: "The sergeant major opens with: ‘I know you all joined because you want to rape, pillage, and kill. That's why I joined. However, you need to think about counterinsurgency.' I was a little taken aback by it, because that's not why I joined."

JEFFREY BROWN: Bergdahl's lead attorney, Eugene Fidell, spoke to the "NewsHour"‘s Dan Sagalyn:

EUGENE FIDELL, Attorney for Bowe Bergdahl: He takes things literally that are said to him. He came into the Army with some ideals, and he had a notion of what the Army was about and what the environment that he was going to be in with was going to be like. And it sounds to me like he was quite surprised to have this kind of guidance.

JEFFREY BROWN: Elsewhere in the transcript, Bergdahl talked of his first mission in Afghanistan, a night patrol in which his job was to look for explosive devices. One of his commanders, he told the Army investigator, yelled at him to speed up the search.

PRODUCER: "Hurry up goes against the common sense. He was just saying, there's a possible mine field in front of you. Hurry up and go hit a mine. That's amazing coming from the person sitting back in the car or in the truck. You're telling me to hurry up in situations I shouldn't be hurrying. That was my first mission. That was my first experience in Afghanistan. And that basically continued."

EUGENE FIDELL: I think that Sergeant Bergdahl expected that his command, that his superiors in the chain of command would be attentive to his personal safety and the personal safety of other members of the unit.

And the kind of instruction or reaction that he got from a fellow soldier in that particular incident displayed an indifference to personnel safety.

JEFFREY BROWN: Later, Bergdahl spoke of the possibility he'd be sent on a suicide mission. It was around this point that he decided to leave the base.

PRODUCER: "What could happen is this battalion commander could see us, my platoon, as this stain on his reputation. Now, sending us on a suicide mission wouldn't be the first in military history. Somebody doing — somebody giving out an order on personal agendas or off personal grievances, it is not going to be a first in military history."

EUGENE FIDELL: Feeling that there was no alternative way to get his concerns about circumstances in the unit and the lack of leadership in the unit, Sergeant Bergdahl concluded that he had to get to a higher echelon. His view was that the way to do that was to walk over land.

JEFFREY BROWN: Nonsense, says former Army lawyer Lieutenant Colonel Geoffrey Corn.

LT. COL. GEOFFREY CORN (RET.), Former Army Lawyer: His concerns over the unit originated long before he ended up on that combat outpost. So what did he do about it? Did he talk to the chaplain? Did he go see the inspector general? Did he try and see any of the superior officers in the chain of command?

Those are all options that a soldier has. Is it possible there were decisions or statements where we say, that might have been a little bit cavalier or maybe a subordinate would have been concerned about what they were being asked to do? Of course. This is the nature of the military. It's the nature of combat operations.

JEFFREY BROWN: Last July, an Army forensic psychiatrist issued a report diagnosing Bergdahl with schizotypal personality disorder, a condition marked by distorted perceptions, eccentric behavior, and magical thinking.

Bergdahl's attorney adds that his client's problems were known earlier, when he was discharged from the Coast Guard, and that he shouldn't have been allowed to enlist in the Army.

EUGENE FIDELL: Sergeant Bergdahl was released prematurely from U.S. Coast Guard boot camp at Cape May, New Jersey, because of a psychological or psychiatric incident. That, in turn, required him to get a waiver in order to be enlisted into the Army. For reasons I'm unable to explain, he was given that waiver. The Army has said, well, we think it was an OK thing to do. That will be an issue at the trial.

JEFFREY BROWN: Geoffrey Corn says Bergdahl's mental state could be a relevant factor in the later part of the court-martial.

LT. COL. GEOFFREY CORN: I think it would be a consideration in sentencing, but it's no surprise that, when the military is trying to fill the ranks in an all-volunteer force in a time where it's hard to bring in the number of recruits they need, that they accept greater risk with the people they bring in, although I do find it somewhat ironic that, based on public information that we have seen, that members of his unit thought that, up to this point, he was a fairly good soldier.

JEFFREY BROWN: In fact, the results of the Bergdahl investigation produced a dramatic split within top Army ranks. The senior Army investigator, Lieutenant General Kenneth Dahl, recommended that Bergdahl not face prison time, saying it would be — quote — "inappropriate."

But in December, a higher official, General Robert Abrams, ruled that a court-martial should go ahead. The trial is tentatively scheduled to start in August. If convicted of all charges, Bergdahl could face life imprisonment.

For the "PBS NewsHour," I'm Jeffrey Brown.

GWEN IFILL: You can read more about what else Bergdahl told the senior Army investigating officer, including the full transcript itself. All that is on our home page, PBS.org/NewsHour.