DoD Knowledge Base: FAQs
In January 2007, the Chairman of the Armed Services Committee, U.S. Senator Carl Levin, set up an investigations unit of the committee staff which spent more than a year-and-a-half conducting the investigation into the origins of detainee abuses. They reviewed hundreds of thousands of documents and conducted extensive interviews of more than 70 individuals, including a number of senior civilian and military officials.
Details of the investigation can be found on Senator Levin's site at: http://www.levin.senate.gov/issues/treatment-of-detainees-in-us-custody.