Three years since his capture, America's only prisoner of war Bowe Bergdahl is still held by the Taliban

A deal to release five Taliban prisoners from Guantanamo Bay has broken down

Almost three years ago, Sergeant Bowe Bergdahl walked off a US army base in eastern Afghanistan, in still unexplained circumstances, into the hands of Taliban kidnappers who promptly released a video of the terrified, tearful 23-year-old pleading to see his family.

The military launched a massive manhunt and residents held vigils in his home town in Idaho. But in intervening years, the trail of the only current US prisoner of war went strangely cold. Claims by the Taliban that Sgt Bergdahl had converted to Islam and was teaching them bomb-making techniques – echoing the fictional POW Sgt Brody in the TV series Homeland – were denied by the Department of Defence.

Sgt Bergdahl's parents have now spoken of their frustration at stalled efforts to free their son, shedding light on the behind-the-scenes diplomacy underway to bring the soldier home.

In the Idaho Mountain Express, Bob Bergdahl said that a deal to release five Taliban prisoners from Guantanamo Bay in exchange for his son's freedom had broken down, his plight caught up in the broader peace negotiations between the US, the Taliban and the Afghan government. "We started out by trying to encourage the Taliban to take care of our son," Mr Bergdahl said. "Now, we're worried that the government isn't concerned enough to put him on the table."

Sgt Bergdahl, described by his parents as compassionate young man who enjoyed cycling and martial arts, had been in Afghanistan for only a few months when he disappeared on 30 June, 2009. Military officials initially said he simply walked off the base in Paktika province. The Taliban said they snatched him as he was ambling around drunk. In the video released after his capture, Sgt Bergdahl said he was kidnapped while on patrol.

Early efforts to get him back failed. Intelligence suggested he had been taken over the border to Pakistan, into the hands of the Taliban-affiliated Haqqani Network. In five videos clips released by the Taliban, Sgt Bergdahl is seen alternately begging for his freedom or condemning military operations in Afghanistan.

The mystery surrounding his fate deepened in August 2010, when The Sunday Times published an interview with an alleged captor who said Sgt Bergdahl had converted, taken on the Islamic name of Abdullah, and was training the Taliban in covert operations and bomb making. In the US drama series Homeland, an American prisoner of war, Sgt Nicolas Brody, returns home after years of captivity to plan an attack on his own country.

The Department of Defence (DoD), however, said reports of Sgt Bergdahl's collusion with the Taliban were pure propaganda. In the last video released in May 2011, Sgt Bergdahl is clean-shaven, which would be unusual for a convert to Islam. Last December, there were reports of a foiled escape bid.

Sgt Bergdahl's fate has been tangled up in the Nato strategy of bringing the Taliban to the table to negotiate some sort of peace between the Islamists and the Afghan government before the full withdrawal of foreign forces in 2014. Those talks collapsed in March when the Taliban said their conditions were not being met, dashing hopes of Sgt Bergdahl's imminent freedom

A DoD spokesman told The Independent that the soldier's safe return remained a "top priority", and Bob Bergdahl said he would continue to press for the release of the Guantanamo Bay fighters in exchange for his son.

In the meantime, he told Reuters, he was learning Pashto, the language of his son's captors, hoping to reach out to them directly: "I feel that I have to do my job as his father."