Boston

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Boston Police officer John Quinn walks with, Miller, his bomb detection canine, over the finish line while sweeping the area in preparation for the Boston Marathon, Wednesday, April 16, 2014, in Boston. (AP Photo/Charles Krupa)

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Massachusetts Emergency Management Agency Director Kurt Schwartz speaks with the media following a news conference in preparation for the Boston Marathon, Wednesday, April 16, 2014, in Boston. (AP Photo/Charles Krupa)

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Boston Police Commissioner William Evans speaks during a news conference in preparation for the Boston Marathon as Massachusetts Emergency Management Agency Director Kurt Schwartz, right, listens, Wednesday, April 16, 2014, in Boston. (AP Photo/Charles Krupa)

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Boston Police Commissioner William Evans, second from left, listens to Boston Marathon Race Director Dave McGillivray during a news conference in preparation for the Boston Marathon, Wednesday, April 16, 2014, in Boston. (AP Photo/Charles Krupa)

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Boston Marathon Race Director Dave McGillivray gestures during a news conference in preparation for the Boston Marathon, Wednesday, April 16, 2014, in Boston. (AP Photo/Charles Krupa)