A hotly disputed US Senate report on torture concluded that waterboarding and other harsh interrogation methods provided no key evidence in the hunt for Osama bin Laden, according to congressional aides and outside experts familiar with the investigation.

However, the CIA still disputes that conclusion.

From the moment of bin Laden's death almost three years ago in what was the United States' biggest counterterrorism success, former Bush administration and some senior CIA officials have cited the evidence trail leading to the al-Qaida mastermind's compound in Pakistan as vindicating the "enhanced interrogation techniques" they authorized after the Sept 11, 2001, attacks.

But Democratic and some Republican senators have disputed that account. They described simulated drownings, sleep deprivation and other such practices as cruel and ineffective. They hope the Senate Intelligence Committee's report on interrogations, renditions and detentions - the release of which is edging closer - will help them make a persuasive case.

The report, congressional aides and outside experts said, examines the treatment of several high-level terror detainees and the information they provided on bin Laden. The aides and people briefed on the report spoke on condition of anonymity because they were not authorized to speak publicly about the confidential document.

The highest-profile detainee linked to the bin Laden investigation was Khalid Sheikh Mohammed, whom the CIA waterboarded 183 times. Mohammed, intelligence officials have noted, confirmed after his 2003 capture that he knew an important al-Qaida courier with the nom de guerre Abu Ahmed al-Kuwaiti.

But the report concludes that such information wasn't critical, according to the aides. Mohammed only discussed al-Kuwaiti months after being waterboarded, while he was under standard interrogation, they said. And Mohammed neither acknowledged al-Kuwaiti's significance nor provided interrogators with the courier's real name.

The debate over how investigators put the pieces together is significant because years later, the courier led US intelligence to the sleepy Pakistani military town of Abbottabad. There, Navy SEALs killed bin Laden in a secret mission.

The CIA has also pointed to the value of information provided by senior al-Qaida operative Abu Faraj al-Libi, who was captured in 2005 and held at a secret prison.

US officials have described how al-Libi made up a name for a trusted courier and denied knowing al-Kuwaiti. Al-Libi, they said, was so adamant and unbelievable in his denial that the CIA took it as confirmation he and Mohammed were protecting the courier.

But the report concludes evidence gathered from al-Libi wasn't significant either, the aides said.

Essentially, they argued, Mohammed, al-Libi and others subjected to harsh treatment confirmed only what investigators already knew about the courier. And when they denied the courier's significance or provided misleading information, investigators would only have considered that significant if they already presumed the courier's importance.

In any case, it still took the CIA years to learn al-Kuwaiti's real identity: Sheikh Abu Ahmed, a Pakistani man born in Kuwait. How the US learned of Ahmed's name is still unclear.

Senator Dianne Feinstein, chairwoman of the intelligence committee, will push to release a summary of the report this week, starting a declassification process that could take several months before any documents are made public.