Washington (CNN) House Speaker John Boehner said Army Sgt. Bowe Bergdahl is "innocent until proven guilty" after the U.S. military charged him with desertion and misbehavior before the enemy, but emphasized in an exclusive interview with CNN's Dana Bash that he was more concerned about the circumstances of his release.

Bergdahl's attorney also released a statement on Wednesday, outlining his defense of the soldier and containing a two-page letter from Bergdahl describing the torture he endured, which included months spent chained to a bed and further years spent chained on all fours or locked in a cage.

Shortly after the charges were announced, Bergdahl's attorneys released a lengthy statement that includes a letter sent to Milley earlier this month outlining their defense of the soldier.

"In light of the nearly five years of harsh captivity Sgt. Bergdahl endured, the purpose of his leaving his unit, and his behavior while a prisoner, it would be unduly harsh to impose on him the lifetime stigma of a court-martial conviction or an other than honorable discharge and to deny him veterans benefits," attorney Eugene R. Fidell writes in the letter.

The statement includes a two-page accounting from Bergdahl of his time in captivity, in which he recounts months spent chained to a bed, then further years spent chained on all fours or locked in a cage.

Bergdahl said for years his body and health declined due to malnourishment, and sores on his wrists and ankles from the shackles grew infected.

"My body started a steady decline in constant internal sickness that would last through the final year," he said.

Bergdahl was frequently beaten, at times with copper wire or a thick rubber hose, and forced to watch Taliban videos, he said. He had no concept of time, and was repeatedly told he would be killed and would never again see his family.

"I was kept in constant isolation during the entire five years, with little to no understanding of time, through periods of constant darkness, periods of constant light, and periods of completely random flickering of light and absolutely no understanding of anything that was happening beyond the door I was held behind," he wrote.

Bergdahl tried a dozen times to escape, he wrote.

In his interview with Bash, Boehner said "like any American, you're innocent until proven guilty."

"And these charges are coming. There will be a trial," Boehner said in an interview taped Wednesday to air Sunday on CNN's "State of the Union."

Boehner said the "more troubling part" of Bergdahl saga is the fact that the U.S. government traded five Taliban fighters for Bergdahl's release, and that recent reports indicate one has returned to the battlefield. He expressed concerns about other detainees held at the U.S. military prison at Guantanamo Bay, which President Barack Obama is working to close, "ending up back on the battlefield and threatening Americans here and abroad."

Obama "violated the law" in failing to alert Congress before the prisoner swap occurred, Boehner added.

"And I still believe that's the more troubling part of this," he said. "We've made clear in the past that we won't negotiate with terrorists, and but yet here we did."

Military officials announced Wednesday afternoon they would charge Bergdahl with one count each of desertion and misbehavior before the enemy.

Bergdahl left his post in Afghanistan before being captured and held captive for five years. For that, he faces charges that carry a maximum penalty of life in a military prison, and he could also have to forfeit pay and be stripped of his rank, Army Col. Daniel King said as he announced the charges.

Bergdahl faces a military procedure similar to a grand jury that will whether charges are appropriate, King said. Then, he could face court martial proceedings.

The decision comes nearly a year after Bergdahl returned to the United States as part of a prisoner exchange and since the Army began a formal investigation into his disappearance from his unit in eastern Afghanistan in June 2009.

The Army concluded its investigation into the circumstances of Bergdahl's capture in December. Until now, it has been in the hands of Gen. Mark Milley, head of U.S. Army Forces Command, who made the decision to charge Bergdahl. Several U.S. military officials CNN has spoken with suggested privately that the process took longer than expected.

Ahead of Wednesday's announcement, officials said Milley only had a few choices. Though the sense had been that Bergdahl must be held accountable for his actions, there had been little appetite for a lengthy term in military confinement given the five years Bergdahl was held by the Taliban.

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Now 28, Bergdahl was taken by the Haqqani terrorist network. But the circumstances of Bergdahl's departure from his base and how willingly he left have not been clear.

King said he couldn't offer those details on Wednesday, and that they're being treated as evidence for the upcoming proceedings against Bergdahl.

Senate Armed Services Committee Chairman John McCain, R-Arizona, called the charges an "important step" on Wednesday.

"This is an important step in the military justice process towards determining the accountability of Sgt. Bowe Bergdahl," he said in a statement. "I am confident that the Department of the Army will continue to ensure this process is conducted with the utmost integrity under the Uniform Code of Military Justice."

Sen. Lindsey Graham, R-South Carolina, meanwhile, lambasted the "unevenness" of Obama's swap of five Taliban prisoners for Bergdahl.

"I wouldn't have done this trade for a Medal of Honor winner," he told CNN. "No military member should expect their country to turn over five Taliban commanders to get their release. Nobody should expect that. It's not the nature of his service that drives my thinking it's just the illogical nature of the swap."

Some members of Bergdahl's platoon have criticized him, labeling Bergdahl a deserter.

"I was pissed off then, and I am even more so now with everything going on," former Sgt. Matt Vierkant, a member of Bergdahl's platoon when he went missing on June 30, 2009, told CNN last year. "Bowe Bergdahl deserted during a time of war, and his fellow Americans lost their lives searching for him."

Bergdahl was freed in May when President Barack Obama agreed to swap five Taliban prisoners who had been detained in Guantanamo Bay to secure Bergdahl's freedom, sending those detainees to Qatar.

Obama announced Bergdahl's release to fanfare in the White House Rose Garden, flanked by the Army sergeant's parents, Bob and Jani Bergdahl. His hometown of Hailey, Idaho, had planned a parade to celebrate Bergdahl's homecoming but later canceled that celebration amid security concerns stemming from the unanswered questions surrounding his disappearance and the resulting controversy over his release.

After returning to the United States, Bergdahl had been on active duty at an administrative job at Fort Sam Houston in San Antonio, Texas. There, the Army assigned Bergdahl a "sponsor" to help him adjust to life in his new post. Upon returning, Bergdahl refused to meet with his parents -- and months later, Army officials had said he was communicating with them but still had not met them face to face.

The five figures the United States exchanged to secure Bergdahl's release were Khair Ulla Said Wali Khairkhwa, Mullah Mohammad Fazl, Mullah Norullah Nori, Abdul Haq Wasiq and Mohammad Nabi Omari. They were mostly mid- to high-level officials in the Taliban regime and had been detained early in the war in Afghanistan because of their positions within the Taliban, not because of ties to al Qaeda.

The detainee swap for Bergdahl has become increasingly controversial in recent weeks after a report published by the office of Director of National Intelligence James Clapper said one of the 17 intelligence agencies operating under its umbrella had judged that a prisoner released in the exchange had since contacted the Taliban.