In December 2001, as the investigation into the U.S. anthrax attacks was gathering steam, coalition soldiers in Afghanistan uncovered what appeared to be an important clue: a trail of documents chronicling an attempt by al-Qaeda to create its own anthrax weapon. The documents told of a singular mission by a scientist named Abdur Rauf, an obscure, middle-aged Pakistani with alleged al-Qaeda sympathies and an advanced degree in microbiology. Using his membership in a prestigious scientific organization to gain access, Rauf traveled through Europe on a quest, officials say, to obtain both anthrax spores and the equipment needed to turn them...