Reuters spoke with sources familiar with the three-year probe, launched by Democrats on the Senate Intelligence Committee, who said investigators dispute claims that torture led to successful counter-terrorism efforts.
Torture methods and enhanced interrogation techniques -- now banned under the Obama administration -- include placing prisoners in stress positions, sleep deprivation and waterboarding, which is simulated drowning. The alleged mastermind of the Sept. 11 terrorist attacks, Khalid Sheikh Mohammed, is said to have been waterboarded 183 times.
A Senate investigator said according to Reuters that there was no evidence that torture had any significant role in the search for Osama bin Laden, who was eventually killed in his Pakistani compound during a U.S. raid one year ago.
The CIA handed over to Intelligence Committee investigators millions of pages of written records charting daily operations of the interrogation program, including graphic descriptions of how and when controversial techniques were employed, Reuters said.
A report on the committee investigation has yet to be finalized, according to Reuters.
The news of its findings was reported ahead of a CBS 60 Minutes interview with a former CIA official who is releasing a book defending the agency's torture methods.
Jose Rodriguez, former head of the CIA's Clandestine Service, maintained in an interview set to air Sunday that torture caused Mohammed and others to give up information on nearly a dozen terrorist plots.
It was the cumulative effect of waterboarding and sleep deprivation and everything else that was done that eventually got to [Mohammed], Rodriguez said, calling him the toughest detainee we had.