Dzhokhar (at left) and Tamerlan Tsarnaev allegedly killed an MIT police officer, carjacked a vehicle and engaged in a gun battle with police soon after authorities distributed this image of the brothers walking near the finish line of the Boston Marathon just before two bombs exploded. Tamerlan, 26, died from injuries he received. Dzhokhar, 19, was captured Friday night. FBI.gov hide caption

itoggle caption FBI.gov

This undated photo provided by Bill Richard, shows his son, Martin Richard, in Boston. Martin Richard, 8, was among the at least three people killed in the explosions, Monday, April 15, 2013, at the finish line of the Boston Marathon. Uncredited/AP/Bill Richard hide caption

itoggle caption Uncredited/AP/Bill Richard