By Jon Herskovitz

SAN ANTONIO (Reuters) - U.S. military prosecutors said in opening statements on Thursday that Army Sergeant Bowe Bergdahl, a former prisoner of war in Afghanistan held for five years before being swapped in 2014 for five Taliban leaders, deliberately left his post.

The prosecutors said at a preliminary hearing to establish probable cause that Bergdahl launched a plan that was weeks in the making and there was sufficient evidence to hold him for trial on charges of desertion and misbehavior before the enemy.

"Under the cover of darkness, he snuck off the post," Major Margaret Kurz, a military prosecutor, said at the hearing held at Joint Base San Antonio-Fort Sam Houston, Texas.

Bergdahl, dressed in his Army service uniform with his hair in a crew cut, has been stationed at the base since shortly after his release in the summer of 2014.

It was his first court appearance since he was charged in March with desertion and misbehavior before the enemy. If convicted of misbehavior, the most serious charge, Bergdahl, 29, could be sentenced to life in prison.

Bergdahl disappeared on June 30, 2009, from Combat Outpost Mest-Lalak in Paktika Province, Afghanistan, and was later captured by the Taliban.

The prosecutors said a search for Bergdahl began with nine men and expanded to a massive effort over about 45 days in difficult terrain. They said Bergdahl sent home personal belongings and told his family to expect something.

The first of three witnesses called by the government, Bergdahl's former platoon leader, described him as a good soldier whose disappearance rocked the unit.

"I was in shock and utter disbelief that I couldn't find one of my men. That is a hard thing to swallow," Captain John Billings told the proceeding.

He said soldiers carrying between 60 and 100 pounds (27 and 45 kg) of equipment hiked through the area, moving from one assignment to another with one overriding objective - finding Bergdahl.

Bergdahl's lawyer Eugene Fidell had a one-line opening statement. "The government should make Sergeant Bergdahl's statements available to the public, not only just to you," he said, referring to statements his client made concerning the incident.

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The Article 32 proceeding is similar to a grand jury investigation under civilian law and both sides can call witnesses and lay out legal arguments.

The presiding officer at the hearing, Lieutenant Colonel Mark Visger, will recommend the course of action for resolving Bergdahl's case, whether it should proceed to a trial by court-martial or be dispensed in some other manner.

Bergdahl was freed in a prisoner swap that sent five Taliban leaders who were being held at Guantanamo to Qatar, where they had to remain for a year. The deal drew heavy criticism from Republicans.

Fidell has said Bergdahl was not trying to desert when he left his post but instead was trying to locate the nearest general officer so he could report "disturbing circumstances."

An initial wave of euphoria over Bergdahl's release was followed by a backlash among U.S. lawmakers angry because they were not given 30 days' notice before the transfer of the Guantanamo prisoners, as required by law.

Some of Bergdahl's former Army comrades also said they believed he deserted his post.

(This story corrects the fourth paragraph to say that Bergdahl has been stationed at the base, not held)





(Reporting by Jon Herskovitz; Additional reporting by David Alexander in Washington; Editing by Eric Beech and Mohammad Zargham)