Julio Cortez / AP Investigators comb through Boylston Street just beyond the finish line of the Boston Marathon. Email Print Share Facebook Tumblr LinkedIn StumbleUpon Reddit Digg Mixx Delicious Google+ (BOSTON) '� The painstaking work to identify a bombing suspect from reams of Boston Marathon footage yielded a possible breakthrough as investigators focused on a man seen dropping off a bag, and then walking away from the site of the second of two deadly explosions. The discovery of the image '� found on surveillance footage from a department store near the finish line '� was detailed by a city politician two days after the attack that left three people dead, wounded more than 170, and cast a dark shadow over one of this city's most joyous traditions. The footage hasn't been made public. President Barack Obama planned to attend an interfaith service honoring the victims Thursday in Boston. There was a heavy police presence around the city's main Roman ...