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. The evidence suggests that the al Qaeda senior leadership was not directly involved or apparently even aware of attack preparations until late stages of planning.
Moreover, there is no evidence that the al Qaeda leadership regarded the use of crude toxins and poisons as being suitable for conducting what would amount to pin prick attacks on the United States; on the contrary, Zawahiri canceled the planned attack
on the New York City subway for "something better," suggesting that a relatively easy attack utilizing tactical weapons would not achieve the goals the al Qaeda leadership had set for themselves.
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