A nearly three-year-long investigation by Senate Intelligence Committee Democrats is expected to find there is little evidence the harsh "enhanced interrogation techniques" the CIA used on high-value prisoners produced counter-terrorism breakthroughs.People familiar with the inquiry said committee investigators, who have been poring over records from the administration of US President George W. Bush, believe they do not substantiate claims by some Bush supporters that the harsh interrogations led to counter-terrorism coups.The backers of such techniques, which include "water-boarding," sleep deprivation and other practices critics call torture, maintain they have led to the disruption of major terror plots and the capture of al-Qaida leaders.One official said investigators found "no evidence" such enhanced interrogations played "any significant role" in the years-long intelligence operations which led to the discovery and killing of Osama bin Laden last May by US Navy SEALs.US President Barack Obama and his aides have largely sought to avoid revisiting Bush administration controversies. But the debate over the effectiveness of enhanced interrogations, which human rights advocates condemn as torture, is resurfacing, in part thanks to a new book by a former top CIA official.In the book, "Hard Measures," due to be published on Monday, April 30, the former chief of CIA clandestine operations Jose Rodriguez defends the use of interrogation practices including water-boarding, which involves pouring water on a subject's face, which is covered with a cloth, to simulate drowning."We made some al-Qaida terrorists with American blood on their hands uncomfortable for a few days," Rodriguez says in an interview with CBS News' "60 Minutes" that will air on Sunday, April 29. "I am very secure in what we did and am very confident that what we did saved American lives."For nearly three years, the Senate intelligence committee's majority Democrats have been conducting what is described as the first systematic investigation of the effectiveness of such extreme interrogation techniques.The CIA gave the committee access to millions of pages of written records charting daily operations of the interrogation program, including graphic descriptions of how and when controversial techniques were employed.Sources agreed to discuss the matter on condition of anonymity because the report has not been finalized.