Who is Bowe Bergdahl?
Bowe Bergdahl is an American soldier, who was serving in Afghanistan.
On June 30, 2009 he was captured by the Taliban-aligned Haqqani network, and held until America agreed to release five members of the Taliban from Guantánamo Bay on May 31, 2014.
At first the homeschooled Buddhist from Idaho was welcomed home as a hero.
But soon America's mood soured.
It emerged that on the night he abandoned the base, he left behind a note saying that he was going away to start a new life, and renounced his American citizenship. He had learnt to speak Pashto, the local language, and made Afghan friends.
He had told one of his friends before arriving in Afghanistan: "If this deployment is lame, I'm just going to walk off into the mountains of Pakistan."
Emails to his parents were published, which showed the contempt he felt for his homeland and the army.
"The US army is the biggest joke the world has to laugh at," he wrote.
"It is the army of liars, back-stabbers, fools, and bullies. I am sorry for everything here. These people need help, yet what they get is the most conceited country in the world telling them that they are nothing and that they are stupid, that they have no idea how to live. We don't even care when we hear each other talk about running their children down in the dirt streets with our armoured trucks. We make fun of them in front of their faces, and laugh at them for not understanding we are insulting them. I am sorry for everything. The horror that is America is disgusting."
How was he captured?
The circumstances surrounding his capture are unclear – and the subject of much speculation.
In a Taliban propaganda video, Bergdahl stated that he was captured when he fell behind on a patrol. But other sources said he simply walked out of the base, and was then captured.
In 2009, the US Department of Defense said his disappearance was due to "walking off his base in eastern Afghanistan with three Afghan counterparts."
Some soldiers who served with Bergdahl called him a deserter, giving interviews and expressing their anger. Nathan Bradley Bethea said there was no patrol happening on the night Bergdahl disappeared, and that Bergdahl had talked about his desire to walk to India.
Another colleague, Cody Full, said: "He knowingly deserted and put thousands of people in danger because he did. We swore to an oath and we upheld ours. He did not."
What happened when he was captured?
The US army launched a huge manhunt to try and find him, and left leaflets across the area asking for help.
The Taliban released a video 18 days after he vanished, showing him in captivity. Several other videos were released over the course of the next five years, in which Bergdahl was filmed pleading with the US military to leave the country.
He twice managed to escape, but was recaptured. He has reportedly told army officials that he was tortured in captivity, and held in darkness in a cage as punishment for escaping.
The Taliban initially asked for a $1 million and the release of 21 Afghan prisoners plus Aafia Siddiqui, a Pakistani scientist convicted of attempted murder of US soldiers in Afghanistan. But then they agreed to the release of five men held in Guantánamo, who were sent to Qatar, and Bergdahl was handed over to the American army.
When he climbed onto the helicopter to take him away, trying to communicate with his rescuers over the roar of the rotors, he wrote “SF?” on a paper plate – asking his rescuers whether they were special forces.
"Yes,” one of the men shouted. “We’ve been looking for you for a long time.”
Bergdahl then burst into tears.
Some soldiers have said that six men were killed during missions to find him. But the Pentagon has said it is impossible to attribute their deaths to Bergdahl's disappearance.
What happened after he was released?
Bergdahl was initially taken for debriefing, before being reunited with his family – his father Bob had even learnt Pashto in his son's absence, in case it helped with negotiations.
President Barack Obama appeared with Bob and Jani Bergdahl in the White House Rose Garden on May 31, 2014, to give the news about the prisoner swap that resulted in the recovery of their son.
Mr Obama said the US has an “ironclad commitment to bring our prisoners of war home” – despite controversy over the prisoner swap, which was never agreed by Congress.
John McCain was reported to be vehemently against the swap, while Hillary Clinton, then Secretary of State, and Leon Panetta, who was then the defence secretary, were lukewarm. John Kerry is said to have supported the deal.
In July 2014 Bergdahl returned to work with the army in San Antonio, Texas. A month later an investigation began.
Why is the hearing taking place?
Because he has now been charged with desertion.
If the hearing decides to send the case to trial, Bergdahl face charges under "Article 85" of the US military code of justice - namely "Desertion with Intent to Shirk Important or Hazardous Duty" and also under Article 99 - "Misbehavior Before The Enemy by Endangering the Safety of a Command, Unit or Place."
If convicted of misbehaviour, the more serious charge, he could be sentenced to life in prison – although military lawyers say that charge could be hard to prove. Desertion carries a five-year sentence.
What does Bergdahl say?
During the army inquiry, he told investigators that he left the base to report on "misconduct in his unit" and that he had intended to return quickly.
Eugene Fidell, Bergdahl's lawyer, said that the solder told him that he "had concerns about certain conditions in the unit and things that happened in the unit and he figured that the only way to get any attention to them would be to get that information to a general officer."
Mr Fidell argued that Bergdahl was absent without permission when he was captured, but he was not a deserter.
Donald Trump has called him a "dirty, rotten traitor" – sparking complaints from Mr Fidell that his client could not get a fair hearing. Not even the army accuse him of treason. Mr Fidell said he was concerned for the safety of Bergdahl, who is so hated by some soldiers that he requires protection.
"In short, it has been 'open season' on SGT Bergdahl," said Mr Fidell, a military law veteran and former president of the National Institute of Military Justice.
"His immediate commander believes he is in physical danger, and therefore has required since last year that he be accompanied by NCOs [non-commissioned officers] whenever he leaves Fort Sam Houston."
Mr Fidell has requested that the army publish a series of documents detailing their investigation, which he says will stop the attacks against Bergdahl.
He wants to have the executive summary of an "AR15-6 report" compiled by Major General Kenneth Dahl, as well as Dahl's extensive interview transcript of Bergdahl, and says both documents are not classified. The army have refused to comment.
He also says there is no suggestion that Bergdahl collaborated with the Taliban.
What can we expect from the hearing?
San Antonio will hold what is termed an Article 32 hearing – a military tribunal to determine whether he should face a court martial.
Lt. Col. Mark Visger, an army lawyer, will conduct the hearing and recommend whether to convene a court martial. The decision ultimately falls to Gen. Robert Abrams, head of Army Forces Command at Fort Bragg, in North Carolina.
Bergdahl or his lawyers will be able to cross-examine witnesses against him and present anything in defence or mitigation. The investigation officer will also examine any witnesses that Bergdahl requests.
The prosecution team, led by Lt Col Christian Beese, a top criminal-law instructor at the Army’s legal academy, and Maj. Margaret Kurz, will argue that Bergdahl left his base to shirk hazardous duties, leading to a manhunt that put many soldiers at risk.
The prosecutors will not, Mr Fidell said, accuse Bergdahl of causing the deaths of any soldiers searching for him.
The hearing is expected to last several days – with some parts of it held behind closed doors.
Jimmy Hatch, now a retired member of the Navy Seals, was hit in the leg by an insurgent’s bullet during a rescue raid days after Bergdahl disappeared, and has had more than 30 operations as a result. He told CNN that Bergdahl deserved his day in court, but that he needed to be held accountable and to understand “how much was risked.”