The Senate report on the CIA’s detention and interrogation program represents the most authoritative and comprehensive finding since the US launched its so-called “war on terror” more than 13 years ago that torture does not work.

The Bush administration and CIA officials involved in the program ... have launched a public relations backlash to the finding, with its own dedicated website. But the sheer bulk and depth of the Senate intelligence committee report will make it much harder to win that argument.

The report finds that CIA detainees subjected to what were then called “enhanced interrogation techniques” either produced no intelligence, or they “fabricated information, resulting in faulty intelligence”. It says that the CIA’s own interrogators “assessed that the most effective method for acquiring intelligence from detainees, including from detainees the CIA considered to be the most ‘high-value’, was to confront the detainees with information already acquired by the intelligence community”.

“This is an authoritative conclusion,” said Philippe Sands, a law professor at University College, London and the author of Torture Team, an account of how torture came to be used increasingly on al-Qaida suspects in the wake of 9/11. “The Senate intelligence commission has been looking into this for several years. I know that they went into it with an open mind. Those who were engaged in the analysis followed the evidence. What it confirmed is what I was always told by US military psychologists, that torture produces information, but it does not produce reliable information.”

In particular, the Senate delivers a verdict on the debate over whether the torture of two senior al-Qaida figures, Abu Zubaydah and Khalid Sheikh Mohammed, forced them to divulge intelligence that prevented further terrorist attacks and thereby saved lives. They were subjected to waterboarding, the pouring of water over a cloth draped over the face to simulate drowning, 83 times in Abu Zubaydah’s case and 183 times in Khalid Sheikh Mohammed’s.

Defenders of waterboarding ... said that its use on Abu Zubaydah led to Khalid Sheikh Mohammed, the mastermind of the 9/11 attacks, and that the latter’s interrogation using waterboarding led to the location and killing of Osama bin Laden. Former vice-president Dick Cheney claimed that the techniques produced “phenomenal” results.

The Senate report refutes those claims.

They had already been denied by former interrogators at the heart of the post-9/11 manhunt. In 2009, a former FBI agent, Ali Soufan, who had taken part in the interrogation of Abu Zubaydah seven years earlier, said that all the useful intelligence came from traditional non-violent questioning, and that his later waterboarding produced nothing further of value.

“Almost all the agency officials I worked with on these issues were good people who felt as I did about the use of enhanced techniques: it is un-American, ineffective and harmful to our national security,” Soufan wrote.

A former official from the US navy’s criminal investigative service, Mark Fallon, wrote on Monday: “As special agent in charge of the criminal investigation task force with investigators and intelligence personnel at Guantánamo Bay, Afghanistan, and Iraq, I was privy to the information provided by Khalid Sheikh Mohammed. I was aware of no valuable information that came from waterboarding.”