Two policemen stand guard as participants pass the starting point of the 9/11 Memorial 5K Run/Walk on the bank of the Hudson River in New York, the United States, April 21, 2013. The activity was held to support the National September 11 Memorial & Museum and encourage volunteerism in honor of those lost on 9/11. (Xinhua/Deng Jian)

Police guard at the starting point of the 9/11 Memorial 5K Run/Walk on the bank of the Hudson River in New York, the United States, April 21, 2013. The activity was held to support the National September 11 Memorial & Museum and encourage volunteerism in honor of those lost on 9/11. (Xinhua/Deng Jian)