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    Boston Marathon explosions

    See images from the scene of the explosions.

  • Boston Marathon explosions

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    An explosion goes off near the finish line of the Boston Marathon on April 15. Two explosions struck the marathon as runners crossed the finish line on Monday, witnesses said, injuring an unknown number of people on what is ordinarily a festive day in the city.
    NBC News
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    Runners continue to run towards the finish line as the second explosion detonates.
    Dan Lampariello / Reuters
  • Boston Marathon explosions

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    A second explosion goes off, in the background, as Bill Iffrig of Lake Stevens, Wash. recovers from being knocked to the ground by the first explosion near the finish line of the Boston Marathon.
    John Tlumacki / The Boston Globe via Getty Images
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    Police officers with their guns drawn hear the second explosion down the street. The first explosion knocked down Bill Iffrig of Lake Stevens, Wash. at the finish line of the 117th Boston Marathon.
    John Tlumacki / The Boston Globe via Getty Images
  • Boston Marathon explosions

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    :A second explosion goes off near the finish line of the 117th Boston Marathon.
    David L. Ryan / The Boston Globe via Getty Images
  • Boston Marathon explosions

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    Police and runners react to an explosion at the finish line during the Boston on April 15, 2013. Two simultaneous explosions ripped through the crowd on Monday, killing and injuring dozens on a day when tens of thousands of people pack the streets to watch the world famous race.
    Ken McGagh / MetroWest Daily News via Reuters
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    People react to an explosion at the Boston Marathon on April 15.
    Kenshin Okubo / The Daily Free Press via AP
  • Boston Marathon explosions

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    Injured people lie on the sidewalk near a barrier at the scene of the first explosion that went off near the finish line.
    John Tlumacki / The Boston Globe via Getty Images
  • Boston Marathon explosions

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    Bystanders help an injured woman at the scene of the first explosion on Boylston Street near the finish line of the Boston Marathon.
    John Tlumacki / The Boston Globe via Getty Images
  • Boston Marathon explosions

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    Medical responders and bystander Carlos Arredondo, center, run an injured man past the finish line following an explosion at the Boston Marathon on Monday.
    Charles Krupa / AP
  • Boston Marathon explosions

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    A couple embraces near the finish line of the Boston Marathon after two explosions killed and injured many people.
    CJ Gunther / EPA
  • Boston Marathon explosions

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    A man lays on the ground after two explosions went off near the finish line of the 117th Boston Marathon.
    David L. Ryan / /The Boston Globe via Getty Images
  • Boston Marathon explosions

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    Medical workers move the injured across the Boston Marathon finish line following an explosion in Boston, on April 15.
    Charles Krupa / AP
  • Boston Marathon explosions

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    A person who was injured in an explosion near the finish line of the Boston Marathon is taken away from the scene in a wheelchair.
    David L. Ryan / The Boston Globe via Getty Images
  • Boston Marathon explosions

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    A person who was injured in an explosion near the finish line of the Boston Marathon is taken away from the scene on a stretcher.
    David L. Ryan / The Boston Globe via Getty Images
  • Boston Marathon explosions

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    Medical workers aid injured people near the finish line of the Boston Marathon following an explosion in Boston on Monday.
    Charles Krupa / AP
  • Boston Marathon explosions

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    A man is loaded into an ambulance after he was injured by one of two bombs exploded during the 117th Boston Marathon near Copley Square on April 15 in Boston.
    Jim Rogash / Getty Images
  • Boston Marathon explosions

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    Women react at Boylston Street and Massachusetts Avenue, frustrated that they were not able to reach their loved ones.
    Bill Greene / Boston Globe via Getty Images Contributor
  • Boston Marathon explosions

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    Medical workers aid injured people at the finish line.
    Charles Krupa / AP
  • Boston Marathon explosions

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    Runner John Ounao cries when he finds friends after several explosions rocked the finish of the Boston Marathon on April 15. The streets were littered with debris and blood and paramedics raced off with stretchers as police locked down the area, witness said. TV footage showed an explosion sending up a white plume of smoke along the sidelines of the race.
    John Mottern / AFP - Getty Images
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    A runner embraces another woman on the marathon route near Kenmore Square after two bombs exploded during the 117th Boston Marathon.
    Alex Trautwig / Getty Images
  • Boston Marathon explosions

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    Blood and debris litter the scene after two explosions occurred during the Boston Marathon.
    Bruce Mendelsoh / AP
  • Boston Marathon explosions

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    A woman kneels and prays at the scene of the first explosion on Boylston Street near the finish line of the Boston Marathon on Monday.
    John Tlumacki / The Boston Globe via Getty Images
  • Boston Marathon explosions

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    Runners who had not finished the race were stopped before the Massachusetts Avenue overpass on Commonwealth Avenue after two explosions went off near the finish line of the Boston Marathon.
    Yoon S. Byun / The Boston Globe via Getty Images
  • Boston Marathon explosions

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    Two men look under bleachers for another device after two explosions went off near the finish line of the Boston Marathon.
    David L. Ryan / The Boston Globe via Getty Images
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    In the Oval Office, President Barack Obama talks on the phone with FBI Director Robert Mueller to receive an update on the explosions that occurred in Boston. Seated with the President are Lisa Monaco, Assistant to the President for Homeland Security and Counterterrorism, and Chief of Staff Denis McDonough.
    Pete Souza / The White House via AFP - Getty Images
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    People comfort each other after the explosions.
    Jessica Rinaldi / Reuters
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    Ken Poole, right, and Eric Uganecz wait for their loved ones to come for them following the bombing at the Boston Marathon. Both were having trouble connecting with loved ones in the confusion that followed the explosion. Poole was worried about a family member who would have been at the finish line waiting for him around the time of the explosion.
    Charlie Mahoney / Prime Collective for NBC News
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    Justine Franco of Montpelier, Vt., holds up a sign near Copley Square in Boston while looking for her missing friend, April, who was running in her first Boston Marathon on Monday.
    Winslow Townson / AP
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    People make phone calls to loved ones at a makeshift AT&T booth with battery chargers following the bombing during the Boston Marathon on April 15.
    Charlie Mahoney / Prime Collective for NBC News
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    A Boston Marathon runner, center, is reunited with loved ones near Copley Square following an explosion in Boston on Monday.
    Winslow Townson / AP
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    One of the blast sites on Boylston Street near the finish line of the Boston Marathon is investigated by two people in protective suits in the wake of two blasts in Boston Monday.
    Elise Amendola / AP
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    Massachusetts Gov. Deval Patrick speaks as Boston Police Commissioner Ed Davis, right center, and FBI Special Agent in Charge Richard DesLauriers, far right, listen at a news conference in Boston regarding two bombs which exploded in the street near the finish line of the Boston Marathon on Monday.
    Elise Amendola / AP
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    A runner retrieves his belongings from a Boston Athletics Association worker at a sorting area near the site of one of the explosions at the Boston Marathon on April 15.
    Michael Dwyer / AP
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    A Boston police officer stands near the scene of a twin bombing at the Boston Marathon, on April 16, 2013 in Boston, Massachusetts..The bombings at the 116-year-old Boston race, resulted in heightened security across the nation.
    Spencer Platt / Getty Images