An American flag waves from a make-shift memorial as police stand guard on Boylston Street, which was still closed to traffic two days after two bomb explosions killed three and wounded 176 at the Boston Marathon in Boston, Massachusetts April 17, 2013. Boston Marathon bombing investigators on Wednesday entered the third day of their hunt with an emerging picture of the target: a suspect or suspects carrying heavy bags or backpacks made of dark nylon. While still unable to conclude whether a group or individuals were responsible for the attacks that killed three people and wounded 176, and whether they were foreign or American, investigators gathered enough evidence at the crime scene on Tuesday to slightly narrow their search. REUTERS/Adrees Latif (UNITED STATES - Tags: CRIME LAW CIVIL UNREST SPORT ATHLETICS TPX IMAGES OF THE DAY)