...The clemency letter provided a harsh critique of the legal framework and C.I.A. detention system that the Bush administration established after the attacks of Sept. 11, 2001, the legacy of which continues today in the form of the wartime prison at Guantánamo Bay now holding Mr. Khan and 38 other detainees. It also offered an unusually candid view of the thinking of some U.S. military officers on the use and value of torture. ...

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