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CNN's Tom Foreman and former FBI assistant director Tom Fuentes discuss three critical time periods in the investigation into Monday's Boston Marathon terror attack.
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CNN's Wolf Blitzer talks to Massachusetts Gov. Deval Patrick about the ongoing bombing investigation in Boston.
RELATED STORY: Sources: Possible suspect sought in Boston bombing
CNN's Sanjay Gupta explains ricin and how deadly the poison can be.
RELATED STORY: Ricin scare rattles Washington