Following Last Year’s Bombing, Thousands Participate in Boston Marathon

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Workers move security gates into position in front of Wellesley College in the early morning before the start of the 118th Boston Marathon, in Wellesley, Mass., April 21, 2014.

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Participants in the wheelchair division of the 118th Boston Marathon start their race, in Hopkinton, Mass., April 21, 2014.

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The second wave of runners make their way down Main Street during the 118th running of the Boston Marathon in Hopkinton, Mass., April 21, 2014.

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Boston police officers, part of the K-9 unit, patrol Boylston Street near the finish line before the start of the 2014 Boston Marathon, Boston, Mass., April 21, 2014.