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Several terrorist groups have actively sought weapons of mass destruction (WMD) of one kind or another. In particular, the Japanese cult group Aum Shinrikyo, al Qaeda and its associates -- notably the Egyptian Islamic Jihad, Jemaah Islamiya and Lashkar al Tayyib -- figure most prominently among the groups that have manifested some degree of intent, experimentation, and programmatic efforts to acquire nuclear, biological and chemical weapons. To date, however, al Qaeda is the only group known to be pursuing a long-term, persistent and systematic approach to developing weapons to be used in mass casualty attacks.

Osama bin Ladin's assertion in 1998 that it was his Islamic duty to acquire weapons of mass destruction ensured that the fulfillment of this intent would become a top...