Two explosions occurred near the finish line at the Boston Marathon on April 15, about four hours after the start of the race. At least three people were killed, and more than 170 were wounded.
Boston Marathon Explosion
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A Boston police officer wheels in injured boy down Boylston Street as medical workers carry an injured runner following an explosion during the 2013 Boston Marathon, April 15, 2013.
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Justine Franco of Montpelier, Vermont, holds up a sign near Copley Square looking for her missing friend, April, who was running in her first Boston Marathon, April 15, 2013.
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President Barack Obama leaves the podium after speaking in the press briefing room at the White House, April 15, 2013, following the explosions at the Boston Marathon.