Concerns were raised in December 2011, partly because of a fear that the research could be misused and become a biological weapon.

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While the Times report said that the attack will involve a biological weapon, one government source said he was not aware of Walker saying anything of the kind.

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This is so even though powerful evidence exists that others around the world, notably the Soviet Union and Iraq, have proceeded to acquire biological weapon capabilities, notwithstanding the convention.

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U.S. officials predicted before the war that at least 100 metric tons of weapon-ready chemical and biological agents would be found.

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Biological weapons experts said the biological agent is extremely difficult to turn into a weapon of mass destruction.

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