Two explosives went off near the finish line of the Boston Marathon in Boston, Mass. on April 15, 2013, killing three and wounding more than 170 people. The victims were identified as 29-year-old Krystle Campbell (left), 8-year-old Martin Richard (center-left) and 23-year-old Lu Lingzi (center-right). Martin, of Dorchester, Mass., was with his family near the finish line waiting for his father to complete the marathon. Campbell, of Medford, Mass., went with her best friend to take a picture of the friend’s boyfriend crossing the finish line. Lu, of Shenyang, China, was a graduate student studying statistics at Boston University. Sean Collier (right), a 26-year-old Massachusetts Institute of Technology police officer, was shot and killed late Thursday night during a confrontation with the two Boston Marathon bombing suspects.