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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
CNN's Joe Johns looks at the nature of the explosives used in the Boston Marathon blasts.
A suspicious letter containing ricin, a poison, was addressed to a senator, according to sources. CNN's Dana Bash reports.
RELATED STORY: Ricin scare rattles Washington
CNN's Wolf Blitzer reports the third victim in the Boston Marathon attack was a Boston University graduate student.
RELATED STORY: Sadness, resolve as Boston comes to grips with deadly marathon bombing
Patty Campbell says Monday's terror attack in Boston doesn't make any sense. Her daughter, Krystle, died in the bombing.
RELATED STORY: 'Boston will overcome,' mayor vows amid bombing investigation
CNN's Tom Foreman takes a closer look at how and where Monday's terror attack in Boston occurred.
RELATED STORY: Boy, 8, one of 3 killed in bombings at Boston Marathon; scores wounded
A photographer captured the two explosions at the Boston Marathon up close.
RELATED STORY: Boy, 8, one of 3 killed in bombings at Boston Marathon; scores wounded