People participate in Boston Marathon Tribute Run
Survivors and first responders of the 2013 Boston Marathon bombing walk down Boylston Street to the marathon finish line during a Tribute Run in Boston, Massachusetts, the United States, April 19, 2014. Twin bombs placed in backpacks near the finish line of Boston Marathon killed three people and injured more than 260 on April 15, 2013. (Xinhua/Yin Bogu)