26 October 2011 Last updated at 04:03 GMT
Pakistan accused of backing Taliban
Pakistan has been accused of playing a double game, acting as America's ally in public while secretly training and arming its enemy in Afghanistan according to US intelligence.
In a prison cell on the outskirts of Kabul, the Afghan Intelligence Service is holding a young man who alleges he was recruited earlier this year by Pakistan's powerful military intelligence agency, the ISI.
He says he was trained to be a suicide bomber in the Taliban's intensifying military campaign against the Western coalition forces - and preparations for his mission were overseen by an ISI officer in a camp in Pakistan.
After 15 days training, he was sent into Afghanistan.
"There were three of us. We were put into a black vehicle with black windows. The police did not stop the car because it was obviously ISI. No-one dares stop their cars. They told me... you will receive your explosive waistcoat, and then go and explode it."Taliban bases in Pakistan
The man recruited to be a suicide bomber changed his mind at the last minute and was later captured by the Afghan intelligence service.
But his story is consistent with a mass of intelligence which has convinced the Americans that, as they suspected, for the last decade Pakistan has been secretly arming and supporting the Taliban in its attempt to regain control of Afghanistan.
These suspicions started as early as 2002, when the Taliban began launching attacks across the border from their bases in Pakistan, but they became more widely held after 2006 when the Taliban's assault increased in its ferocity, not least against the ill-prepared British forces in Helmand province.
The final turning point in American eyes was the attack on Mumbai when 10 gunmen rampaged through the Indian city, killing 170 people - two weeks after Barack Obama's US presidential election victory in November 2008.
Despite Pakistan claiming it played no part in the attack, the CIA later received intelligence that it said showed the ISI were directly involved in training the Mumbai gunmen.
President Obama ordered a review of all intelligence on the region by a veteran CIA officer, Bruce Riedel.
"Our own intelligence was unequivocal," says Riedel. "In Afghanistan we saw an insurgency that was not only getting passive support from the Pakistani army and the Pakistani intelligence service, the ISI, but getting active support."Training and supplies
Pakistan has repeatedly denied the claims. But the BBC documentary series Secret Pakistan has spoken to a number of middle-ranking - and still active - Taliban commanders who provide detailed evidence of how the Pakistan ISI has rebuilt, trained and supported the Taleban throughout its war on the US in Afghanistan.
"For a fighter there are two important things - supplies and a place to hide," said one Taliban commander, who fights under the name Mullah Qaseem. "Pakistan plays a significant role. First they support us by providing a place to hide which is really important. Secondly, they provide us with weapons."
Another commander, Najib, says: "Because Obama put more troops into Afghanistan and increased operations here, so Pakistan's support for us increased as well."
He says his militia received a supply truck with "500 landmines with remote controls, 20 rocket-propelled grenade launchers with 2000 to 3000 grenades... AK-47s, machine-guns and rockets".Pakistani military
Evidence of Pakistan's support for the Taliban is also plain to see at the border where insurgents are allowed to cross at will, or even helped to evade US patrols.
And the recent drone attacks in Pakistan have become increasingly effective as intelligence has been withheld from the Pakistanis, claims Mr Riedel.
"At the beginning of the drone operations, we gave Pakistan an advance tip-off of where we were going, and every single time the target wasn't there anymore. You didn't have to be Sherlock Holmes to put the dots together."
Osama Bin Laden's capture and killing followed this same model - the Americans acting on their own, to the humiliation of Pakistan. Trust between the two supposed allies has never been lower.
Bin Laden was the reason America had attacked Afghanistan and overthrown the Taliban who had always refused to hand him over. His death has removed a major obstacle to peace.
But those who claim that Pakistan's hidden hand has shaped the conflict fear the same is now true of the negotiations for peace. Last year, in the Pakistani city of Karachi, Mullah Baradar, the Taliban's second-in-command, was captured by the ISI.
Secretly, Baradar had made contact with the Afghan government to discuss a deal that would end the war. He had done so without the ISI's permission and he was detained "to bring him back under control" according to one British diplomat.
More recently, Hawa Nooristani, a member of Afghanistan's High Peace Council, says she was called to a secret meeting.
Waiting for her was a commander from the most lethal faction of the Taliban, the Haqqani network, which first brought suicide bombing to Afghanistan. To her astonishment he said he wanted peace talks.
"He said it was vital Pakistan intelligence knew nothing of the meeting. He said not to disclose it because Pakistan does not want peace with Afghanistan and even now they are training new Taleban units.
"He was also scared that the Pakistanis will arrest him because he lives in Pakistan and he said it would be easy for them to arrest him."
The Afghan government began peace talks with the Taliban but these were abandoned after its chief negotiator, former President Rabbani, was killed by a suicide bomber purporting to be a Taliban envoy.
Any future peace will have to be concluded with Pakistan President Karzai has since declared
To American policy advisers like Bruce Riedel, the message is clear:
"The ISI may not be able to deliver the Taliban to the negotiating table, but they can certainly spoil any negotiations process. So far, there's very little sign, that I've seen, that Pakistan is interested in a political deal."
While denying links to the Taliban, Pakistan insists that it is doing no more than what any country would do in similar circumstances.
"We cannot disregard our long term interest because this is our own area," said General Athar Abbas, chief spokesman for Pakistan's military.
US Secretary of State Hillary Clinton said during a recent visit to Pakistan: "The Pakistanis have a role to play, they can either be helpful, indifferent or harmful."
But there are those like Mr Riedel who fear that the forces unleashed in 10 years of war may yet come to haunt the whole world:
"There is probably no worse nightmare, for America, for Europe, for the world, in the 21st Century than if Pakistan gets out of control under the influence of extremist Islamic forces, armed with nuclear weapons...The stakes here are huge."
What happens in Pakistan may yet be the most enduring legacy of 9/11 and the hunt for Bin Laden.
Secret Pakistan is on BBC Two at 9pm on Wednesday 26 October and Wednesday 2 November or watch online afterwards (UK only) via BBC iPlayer.