The Senate Armed Services Committee began an inquiry in January 2007, into "the origins of aggressive interrogation techniques used against detainees in U.S. custody." The inquiry concluded in December 2008 with its executive report and conclusions.
Senator Carl Levin's website includes documentation of the inquiry, including:
Part I: The Origins of Aggressive Interrogation Techniques, June 17, 2008.
Part II: Opening Statement by Senator Carl Levin, Senate Armed Services Committee Hearing on the Authorization of SERE Techniques for Interrogations in Iraq, September 25, 2008.
Report on Inquiry into the Treatment of Detainees in U.S. Custody, approved in November 2008, released on April 21, 2009: details the military's use of harsh interrogation techniques on detainees accused of terrorism and shows that these techniques were given approval by top Bush administration officials. The report covers military (not CIA) interrogations.
Senate Armed Services Committee Inquiry Into the Treatment of Detainees in U.S. Custody: Conclusions, released December 11, 2008: at the release of the conclusions and executive summary, Senator John McCain stated, "The Committee's report details the inexcusable link between abusive interrogation techniques used by our enemies who ignored the Geneva Conventions and interrogation policy for detainees in U.S. custody. These policies are wrong and must never be repeated." Chairman Carl Levin said, "The abuses at Abu Ghraib, GTMO and elsewhere cannot be chalked up to the actions of a few bad apples. Attempts by senior officials to pass the buck to low ranking soldiers while avoiding any responsibility for abuses are unconscionable. The message from top officials was clear; it was acceptable to use degrading and abusive techniques against detainees. Our investigation is an effort to set the record straight on this chapter in our history that has so damaged both America's standing and our security. America needs to own up to its mistakes so that we can rebuild some of the good will that we have lost."