Bowe Bergdahl sneaked out of a US military command post carrying water, a knife, a notebook, money and a disguise in a carefully-planned act of desertion, a prosecutor claimed on Thursday at the start of a hearing to decide whether the army sergeant should face a court martial.

Major Margaret Kurz told the hearing that Bergdahl meticulously organised and carried out an unauthorised exit from the base in eastern Afghanistan on 30 June, 2009 – putting his affairs in order and laying out his possessions on his sleeping area then leaving under cover of darkness.

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Bergdahl was charged in March with desertion and the rare charge of misbehaviour before the enemy, which carries a sentence of up to life in prison. Desertion can result in a maximum five-year prison sentence.

Prosecutors began making their case against him in a courtroom at Fort Sam Houston in what is known as an Article 32 hearing. The presiding officer, lieutenant colonel Mark Visger, will decide whether there is probable cause to charge the 29-year-old from Idaho with breaking military rules.

Visger will make a recommendation to general Robert Abrams, the head of US army forces command in Fort Bragg, North Carolina, who will ultimately determine how to proceed in the case.

Bergdahl was captured by the Taliban and held for five years. The case became a political controversy because he was released in exchange for five Taliban leaders who were being held by the US at Guantánamo Bay. The Obama administration was criticised for failing to notify Congress about the deal.

Some members of Bergdahl’s former unit have said he should be severely punished, claiming that six soldiers died, directly or indirectly, as part of search efforts. Before his disappearance, Bergdahl reportedly expressed misgivings about the US military’s role in Afghanistan and his own part in the conflict.

The government’s first witness was Bergdahl’s platoon commander at the time of his disappearance, captain John Billings. He said that Bergdahl was “a great soldier from all accounts” who “always did everything I asked him to do, never complained … no issues”.

Billings testified that when he was woken up early on the morning of 30 June and told that Bergdahl had vanished, he thought it was a practical joke. “These guys are messing with me,” he recalled thinking. But the seriousness of the situation quickly became clear.

“I was in shock, absolute utter disbelief that I couldn’t find one of my men,” he said. “There were a myriad of emotions that were just crushing me inside because I couldn’t find my guy.”

Billings described the tough conditions and tedious work at the small, basic, Observation Post Mest, and the frantic attempts to find Bergdahl, which went on until the end of August and exposed his unit to potential danger, he said – though he denied that any of his men were killed during the search.

The army set up checkpoints and roadblocks and searched villages. Billings said that he and his soldiers were outside the post for 19 successive days looking for Bergdahl, searching for 19-20 hours a day while carrying up to 100 pounds of equipment in 90-100F heat.

Changes of clothes were in such short supply that Billings said he wore the same uniform for days even though it was soiled after he contracted dysentery. Some soldiers ripped their socks and T-shirts to use as toilet paper.

On cross-examination, Billings said that he was unaware that Bergdahl had any mental health problems. A defence attorney told the hearing that he had required a waiver to join the army having been discharged early from the Coast Guard, and that an army psychiatric analysis had found that he had a severe mental disease or defect.

In the afternoon session, the company commander, Major Silvino Silvino, said that after spending 45 days searching for the missing man, soldiers were angry and “worn out, beat down, there were injuries from [explosive devices] that took its toll.” He said that many vehicles had been damaged by wear and tear or bombs and that the incident had harmed Blackfoot Company’s reputation, leading to gibes within the army that “they lose people”.

Other than at the start to say he understood the charges against him, Bergdahl did not speak in the opening session of the hearing, which took place in a windowless, low-ceilinged conference room in the basement of a building at the fort near downtown San Antonio. Wearing a blue army dress uniform, he sat upright at a table, flanked by his legal team, paying close attention.

Bergdahl’s lead attorney, Eugene Fidell, has questioned whether his client can get a fair trial given public criticism of his behaviour – not least from the leading Republican presidential candidate, Donald Trump, who in a speech last month called him a “dirty, rotten traitor”.

In March, Fidell wrote to Mark Milley, a general who oversaw the case, complaining that “while many Americans have taken a broader and more sympathetic view, the depth and breadth of the current hostility to Sergeant Bergdahl are extraordinary and have enveloped the case with a lynch mob atmosphere”.

The hearing continues.