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Runners carry flags as they approach the finish line after completing the final mile of the Boston Marathon course during "#onerun" in Boston, Massachusetts, May 25, 2013. REUTERS/Dominick Reuter ( USA/ )

A runner does a plank as others cross the finish line after completing the final mile of the Boston Marathon course during "#onerun" in Boston, Massachusetts, May 25, 2013. REUTERS/Dominick Reuter ( USA/ )

Runners who were unable to finish the Boston Marathon on April 15 because of the bombings head toward the finish line on Boylston Street after the city allowed them to finish the last mile of the race in Boston, Saturday, May 25, 2013. (AP Photo/Winslow Townson) ( Boston Marathon Last Mile )

Katie Eastman (L) and Kiaren Shaughnessy visit the memorial on Copley Square after crossing the finish line and completing the final mile of the Boston Marathon course during "#onerun" in Boston, Massachusetts, May 25, 2013. Eastman participated in the marathon but was unable to finish when the course was shut down following the bombing attack. The event was organized to give athletes and spectators an opportunity to complete the final mile of the Marathon that was cut short when two bombs exploded at the finish line. REUTERS/Dominick Reuter ( USA/ )

Runners carry American flags and a Chinese flag as they approach the finish line after completing the final mile of the Boston Marathon course during "#onerun" in Boston, Massachusetts, May 25, 2013. REUTERS/Dominick Reuter ( USA/ )

Runners who were unable to finish the Boston Marathon on April 15 because of the bombings cross the finish line on Boylston Street after the city allowed them to finish the last mile of the race in Boston, Saturday, May 25, 2013. (AP Photo/Winslow Townson) ( Boston Marathon Last Mile )

Maxwell Surprenant, right, and Emily Perron hold up signs cheering on runners who were unable to finish the Boston Marathon on April 15 because of the bombings after the city allowed them to finish the last mile of the race in Boston, Saturday, May 25, 2013. (AP Photo/Winslow Townson) ( Boston Marathon Last Mile )

Runners who were unable to finish the Boston Marathon on April 15 because of the bombings cross the finish line on Boylston Street after the city allowed them to finish the last mile of the race in Boston, Saturday, May 25, 2013. (AP Photo/Winslow Townson) ( Boston Marathon Last Mile )

Runners cross the finish line after completing the final mile of the Boston Marathon course during "#onerun" in Boston, Massachusetts, May 25, 2013. REUTERS/Dominick Reuter ( USA/ )

Runners (L-R) Kyle Shade, Andrew Truco, and Boston City Councillor Mike Ross hold their flags as runners cross the finish line after completing the final mile of the Boston Marathon course during "#onerun" in Boston, Massachusetts, May 25, 2013. REUTERS/Dominick Reuter ( USA/ )

Rachel, left, and Pam Vingsness of Newton, Mass., hug each other after crossing the finish line as runners who were unable to finish the Boston Marathon on April 15 because of the bombings were allowed to finish the last mile of the race in Boston, Saturday, May 25, 2013. (AP Photo/Winslow Townson) ( APTOPIX Boston Marathon Last Mile )

Joey and Chanel Sovine wait for runners to cross the finish line after completing the final mile of the Boston Marathon course during "#onerun" in Boston, Massachusetts, May 25, 2013. REUTERS/Dominick Reuter ( USA/ )

Erin Roy (L) comforts Elise Wulff as runners cross the finish line after completing the final mile of the Boston Marathon course during "#onerun" in Boston, Massachusetts, May 25, 2013. Wulff participated in the marathon but was unable to finish when the course was shut down following the bombing attack. REUTERS/Dominick Reuter ( USA/ )

Runners cross the finish line after completing the final mile of the Boston Marathon course during "#onerun" in Boston, Massachusetts, May 25, 2013. T REUTERS/Dominick Reuter ( USA/ )

Kelly D'Amaro and her daughters visit the memorial on Copley Square after crossing the finish line and completing the final mile of the Boston Marathon course "#onerun" in Boston, Massachusetts, May 25, 2013. D'Amaro participated in the marathon but was unable to finish when the course was shut down following the bombing attack. REUTERS/Dominick Reuter ( USA/ )

Runners who were unable to finish the Boston Marathon on April 15 because of the bombings pass the first bombing site as they head toward the finish line on Boylston Street after the city allowed them to finish the last mile of the race in Boston Saturday, May 25, 2013. (AP Photo/Winslow Townson) ( Boston Marathon Last Mile )

Rachel, left, and Pam Vingsness of Newton, Mass., hug each other after crossing the finish line as runners who were unable to finish the Boston Marathon on April 15 because of the bombings were allowed to finish the last mile of the race in Boston, Saturday, May 25, 2013. (AP Photo/Winslow Townson) ( Boston Marathon Last Mile )

Pam Vingsness is greeted by her daughter Rachael at the finish line after completing the final mile of the Boston Marathon course during "#onerun" in Boston, Massachusetts, May 25, 2013. Pam participated in the marathon but was unable to finish when the course was shut down following the bombing attack.REUTERS/Dominick Reuter ( USA/ )

Pam Vingsness, right, comforts her crying mother, Rachel, of Newton, Mass., after they crossed the finish line, as runners who were unable to finish the Boston Marathon on April 15 because of the bombings were allowed to finish the last mile of the race in Boston, Saturday, May 25, 2013. (AP Photo/Winslow Townson) ( APTOPIX Boston Marathon Last Mile )