The CIA misled the White House and public about its torture of detainees after the September 11 attacks and acted more brutally and pervasively than it acknowledged, a US Senate report said on Tuesday, drawing calls to prosecute American officials.
The Senate Intelligence Committee's five-year review of 6.3 million pages of CIA documents concluded that the intelligence agency failed to disrupt a single plot despite torturing al Qaeda and other captives in secret facilities worldwide between 2002 and 2006, when George W Bush was president.
The CIA interrogation programme was devised by two agency contractors to squeeze information from suspects after the attacks on September 11, 2001. The interrogations took place in countries that included Afghanistan, Poland and Romania.
Some captives were deprived of sleep for up to 180 hours, at times with their hands shackled above their heads, and the report recorded cases of simulated drowning or "waterboarding" and sexual abuse, including "rectal feeding" or "rectal hydration" without any documented medical need.
It described one secret CIA prison, its location not identified, as a "dungeon" where detainees were kept in total darkness and shackled in isolated cells, bombarded with loud noise and given only a bucket in which to relieve themselves.
Committee chair Dianne Feinstein, speaking on the Senate floor after releasing the report, said the techniques in some cases amounted to torture and that "the CIA's actions, a decade ago, are a stain on our values, and on our history."
The UN's special rapporteur on human rights and counter-terrorism, Ben Emmerson, said the report revealed a "clear policy orchestrated at a high level within the Bush administration" and called for prosecution of US officials.
Civil rights advocates also called for accountability.
"Unless this important truth-telling process leads to prosecution of the officials responsible, torture will remain a 'policy option' for future presidents," said Kenneth Roth, executive director of Human Rights Watch in New York.
The CIA dismissed the findings, saying its interrogations secured valuable information. Many Republicans criticised the decision by Democratic lawmakers to release the report, which was put together by the committee's Democratic majority, saying it would put Americans at risk.
The report found the techniques used were "far more brutal" than the CIA told the public or policymakers. Before the report's release, the United States boosted security at its military and diplomatic facilities abroad.
The report said the CIA had tried to justify its use of torture by giving examples of what it called "thwarted" terrorist plots and suspect captures, but the "representations were inaccurate and contradicted by the CIA's own records."
Despite the calls for accountability, there seemed little prospect of criminal prosecutions of those who implemented the programme, or measures to hold politicians who authorised it accountable.
A law enforcement official said the US Justice Department had no plans to conduct any investigation of the CIA's actions.
Intelligence officials said that at one point, the Justice Department, through a specially designated prosecutor, conducted a criminal investigation into around 20 cases of allegations the CIA abused detainees. However, that investigation was closed without charges being filed.
President Barack Obama signalled he was more interested in focusing on the future than reopening a dark and contentious period from the country's recent past.
While in office Bush's vice president, Dick Cheney, and other Bush administration officials said the "harsh interrogation" programme was justified by results that included halting plots and catching terrorists.
Bush ended many aspects of the programme before leaving office, and Obama swiftly banned "enhanced interrogation techniques" after his 2009 inauguration.
The report says CIA records showed that seven of 39 CIA detainees subjected to harsh interrogations produced no intelligence at all while in CIA custody. Others made up stories, "resulting in faulty intelligence".
The CIA had failed to use adequately trained and vetted personnel, the report said. The two psychologists contracted to set up the programme and run it had no experience in interrogation or specialised knowledge of al Qaeda.
The report accuses the CIA of failing to thoroughly brief Bush about the interrogation techniques. Senate investigators said official records suggested that while the CIA planned to brief Bush in 2002, the White House subsequently told the agency Bush was not getting the briefing.
Investigators say Bush was not fully briefed on the programme until 2006, around the time he shut it down, and expressed discomfort at learning the full details. In his memoirs Bush said he had been briefed on the programme.
Republican Senator John McCain, who was tortured as a prisoner of war in Vietnam in the 1960s, said Americans were entitled to the truth about the programme and its disclosure that such methods were ineffective.