President Barack Obama has called waterboarding torture
In making Licence to Torture, Panorama did not set out to ask whether the US practices adopted in the aftermath of 9/11 were right, wrong, justified or fruitful. We aimed to find out if they broke US and international law.
One might think that in the world's most powerful democracy this would be the central public debate. But not in America. The debate that dominates here today is whether torture worked.
At a public forum at a southern California college, we tracked down one of the legal architects of the Bush interrogation programme, a man named John Yoo.
He pointed out that the legal advice that he and other senior lawyers in the Bush administration wrote were not policy recommendations.
Still, Mr Yoo defended the harsh interrogation techniques.
"Was it worth it?" Yoo asked the crowd rhetorically. "Well, we haven't had an attack in seven years."
The audience burst into applause.
There is a significant number of Americans who are sickened by the Bush administration's interrogation tactics, but many are unsure if they want to see prosecutions.
It came as little surprise that our project, looking into the question of guilt, was not popular with some CIA and White House insiders. Nevertheless we were granted extraordinary access to a large number of key individuals who helped piece together the story, mostly off camera.
As we ploughed through legal memos, court cases, government reports and books and talked to lawyer after lawyer, it emerged that a central legal question was this: Did America's leaders intend to torture?
There was a real sense that there was going to be a major new attack that was going to come and that we needed to somehow prevent it
John Bellinger Former legal adviser, US National Security Council
Did the White House approve torture "by accident", because their lawyers decided that waterboarding and confining someone in a box was not actually torture?
Or was there a policy and an intent to torture behind it all?
In investigations of this nature, the answer lies in the detail. In this case, chronology was the key.
America's leaders say they only authorised the controversial techniques because their lawyers advised that they did not constitute torture. It therefore became critical for us to find out if the torture started before the key legal memos were issued.
We spoke to several people who we believed knew this very precise piece of information. But so often in our inquires, the answer came back: "I cannot recall."
Then we met John Kiriakou, the former CIA operative who had led the capture of key al-Qaeda suspect Abu Zubaydah in 2002. He had flown back to the US shortly after the capture and monitored Abu Zubaydah's interrogation from CIA headquarters in Virginia.
Kiriakou was categorical that Abu Zubaydah was waterboarded in the early summer of 2002. This became a crucial piece for the Panorama team in the puzzle that we were slowly piecing together, because the key legal memos that approved the method were not issued until August 2002.
John Kiriakou: 'All took place before 1 August'
The CIA has told the BBC that waterboarding did not happen before that August 2002 memo but would not reveal when it did occur.
It is not clear that any oral legal advice that told White House leaders that the harsh techniques were not torture before August would amount to much of a legal defence in court.
For more than 50 years, waterboarding has been considered torture in America, and torture is illegal.
Abu Zubaydah was strapped to a board, with his face partially covered, while water was poured onto his nose and mouth.
Abu Zubaydah remains in custody in Guantanamo Bay
According to his lawyer, the detainee had begun to drown until they stopped. This happened at least 82 more times.
It has emerged partly from newly-released government legal memos that the CIA borrowed some of its new interrogation techniques from a secretive US military programme called SERE (Survival, Evasion, Resistance and Escape).
The SERE programme teaches American soldiers how to cope in captivity. Amongst other training techniques, it simulates torture used by the Chinese on American soldiers in Korea in the 1950s.
These methods were intended for training US soldiers, not for use in the interrogation of enemy suspects.
But a recent report by the Senate Armed Service Committee traces how Donald Rumsfeld's Department of Defense, in parallel with the CIA, also contacted the SERE programme, and modelled its interrogation plans on the same techniques.
The Pentagon says SERE techniques were never authorised.
Post 9/11 reality
All this has left many in America asking themselves how they got to this point in the first place?
The reality is that on 11 September 2001 the CIA had virtually no interrogation capacity but, the BBC was told, the agency was rapidly authorised by President Bush to set up a detention and interrogation programme anyway.
A senior CIA insider said they trawled intelligence agencies worldwide in the hunt for new techniques. SERE was contacted as part of this.
Donald Rumsfeld, it was suggested, pushed for his own tough programme.
"Rumsfeld needed intelligence and he didn't trust the CIA", said Lawrence Wilkerson, chief of staff to Colin Powell, former US secretary of state.
Critically, there was distressing intelligence in the aftermath of 9/11 that another attack was imminent.
"There was a real sense that there was going to be a major new attack that was going to come and that we needed to somehow prevent it," said John Bellinger who at the time was legal adviser to the National Security Council.
Insiders say the resulting atmosphere in the White House was that extraordinary measures were called for.
Within months the Bush administration announced that the Geneva Conventions, which ban cruel and degrading treatment, did not apply to suspected members of al-Qaeda.
This sent shock waves around the world.
Obama may decide to prosecute government legal advisers
William Taft, who was Colin Powell's lawyer, drafted a memo arguing that detainees be treated humanely in accordance with article three of the Geneva Conventions, but he said his memo was blocked by the administration.
"I really do think at that time that the reason that they didn't approve publishing my memo was that they intended to actually use coercive techniques," said Mr Taft.
The Bush administration said it was committed to humane treatment along the lines of Geneva, as long as it was consistent with "military necessity", a significant caveat.
"The decision was that the rules were gone" said Mr Taft.
Department of justice lawyers began to prepare legal memos that redefined torture in terms broad enough to allow harsh interrogation techniques, including waterboarding.
With the legal ground dramatically altered, widespread use of controversial interrogation techniques and systematic abuses appeared across US military bases.
Later, concern mounted inside the administration. John Bellinger, who believes existing international law is poorly equipped to deal with al-Qaeda, nevertheless worried that applying none of the Geneva conventions left a large legal grey area.
"I said well if the Geneva conventions in their entirety don't apply, that we need to conclude that something does apply because we are a nation of laws, we're not just a nation of men and of policies".
Panorama has been told by other insiders that President Bush personally authorised the CIA's interrogation programme soon after 9/11, and that he may have personally approved the specific programme by the early summer of 2002.
The net of responsibility could go much wider. The CIA says that over the years more than 50 members of Congress were briefed on elements of the CIA's tactics. Objections were few. But exactly what Congress was told and when is hotly disputed, particularly with recent allegations that the CIA misled Congress during the Bush era.
The Obama administration has not ruled out criminally investigating the lawyers involved in all this. Even interrogators who may have acted beyond the controversial legal advice could face investigation. A major CIA watchdog report with more information, is due to be released this summer.
But with mounting evidence pointing to fundamental responsibility at a very high level, President Obama appears little inclined to pursue anyone who was senior.
Panorama: Licence to Torture, BBC One, Monday 13 July at 2030 (1930 GMT).
This page is best viewed in an up-to-date web browser with style sheets (CSS) enabled. While you will be able to view the content of this page in your current browser, you will not be able to get the full visual experience. Please consider upgrading your browser software or enabling style sheets (CSS) if you are able to do so.