The Boston Marathon

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A crowd gathers at the finish line of the Boston Marathon in Boston for a Sports Illustrated photo shoot to commemorate the one-year anniversary of the Boston Marathon bombings, Saturday, April 12, 2014. (AP Photo/Michael Dwyer)

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Boston Mayor Marty Walsh, center, poses with first-responders, survivors and at least 2000 other people at the finish line of the Boston Marathon in Boston, Saturday, April 12, 2014. The crowd gathered for a Sports Illustrated photo shoot to commemorate the one-year anniversary of the Boston Marathon bombing. (AP Photo/Michael Dwyer)

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Photographer Gregory Heisler, center right, sets up in front of a crowd gathered at the finish line of the Boston Marathon in Boston for a proposed Sports Illustrated cover photo to commemorate the one-year anniversary of the Boston Marathon bombings, Saturday, April 12, 2014. (AP Photo/Michael Dwyer)

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A crowd gathers at the finish line of the Boston Marathon in Boston for a Sports Illustrated photo shoot before the one-year anniversary of the Boston Marathon bombings, Saturday, April 12, 2014. (AP Photo/Michael Dwyer)

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House Homeland Security Committee Chairman Rep. Michael McCaul, Texas Republican (Associated Press) **FILE**

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Watertown, Mass. Police Chief Edward Deveau, left, talks with Watertown Police Sgt. Jeffrey Pugliese, on Capitol Hill in Washington, Wednesday, April 9, 2014, before they testified at the House Homeland Security Committee hearing about the Boston Marathon Bombings leading up to the year anniversary of the attack. (AP Photo/Jacquelyn Martin)

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House Homeland Security Committee Chairman Rep. Michael McCaul, R-Texas, left, holds a document about the Boston Marathon Bombing by Harvard Professor Herman “Dutch” Leonard, right, on Capitol Hill in Washington, Wednesday, April 9, 2014, prior to the start of the committee's hearing on the bombings leading up to the year anniversary of the attack. (AP Photo/Jacquelyn Martin)

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Watertown, Mass. Police Sgt. Jeffrey Pugliese, right, listens to testimony on Capitol Hill in Washington, Wednesday, April 9, 2014, during a Homeland Security Committee hearing about the Boston Marathon Bombings leading up to the year anniversary of the attack. (AP Photo/Jacquelyn Martin)

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Boston Police Department commissioner and current fellow at Harvard University Edward Davis, testifies on Capitol Hill in Washington, Wednesday, April 9, 2014, before the House Homeland Security Committee hearing on the Boston Marathon Bombings leading up to the year anniversary of the attack. (AP Photo/Jacquelyn Martin)

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Watertown, Mass. Police Chief Edward Deveau testifies on Capitol Hill in Washington, Wednesday, April 9, 2014, before the House Homeland Security Committee hearing about the Boston Marathon Bombings leading up to the year anniversary of the attack. (AP Photo/Jacquelyn Martin)