U.S. President Barack Obama joins other public officials and religious leaders gathered in Boston for an interfaith memorial service for the victims of the Boston Marathon bombings earlier this week. The service, called the "Healing of our City," was held at Boston's Cathedral of the Holy Cross.
Boston Honors Bombing Victims
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A memento of flowers in a running shoe rests at a makeshift memorial in Boston's Back Bay neighborhood, April 18, 2013, a few blocks from the finish line of the Boston Marathon.
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Homeland Security Secretary Janet Napolitano testifies on Capitol Hill in Washington, April 18, 2013, before the House Homeland Security Committee. Napolitano says the FBI wants to speak with two men seen in at least one video from the Boston Marathon, but she says she isn't calling them suspects.
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A line of investigators is form as they enter a building adjacent to one of the blast sites near the Boston Marathon finish line, in Boston, April 18, 2013.
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Investigators inspect the area between the two blast sites near the Boston Marathon finish line, Thursday, April 18, 2013, in Boston. Boston remained under a heavy security presence, with scores of National Guard troops gathering among armored Humvees in