The Boston Marathon

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Former Boston Police Commissioner Ed Davis, right, leans in to speak to former Boston Mayor Thomas Menino during a break in a forum entitled, "Leading Cities Through Crisis: Lessons from the Boston Marathon" held at Boston University in Boston, Monday, March 24, 2014. (AP Photo/Elise Amendola)

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Former Boston Mayor Thomas Menino listens during a forum entitled, "Leading Cities Through Crisis: Lessons from the Boston Marathon" held at Boston University in Boston, Monday, March 24, 2014. (AP Photo/Elise Amendola)

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** FILE ** Carlos Arredondo (left) rushed to help Jeff Bauman after the Boston Marathon bomb attack on April 15, 2013. (Associated Press)

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This combination of images released by the FBI on Thursday, April 18, 2013, show two images taken from surveillance video of Dzhokhar (left) and Tamerlan Tsarnaev (right) as they walk near each other through the crowd before the explosions at the Boston Marathon on Monday, April 15, 2013. (AP Photo/FBI)

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Boston Marathon bombing suspect Dzhokhar Tsarnaev id charged with using a weapon of mass destruction in the bombings on April 15, 2013 near the finish line of the Boston Marathon. (AP Photo/Federal Bureau of Investigation) ** FILE **