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 — emerged 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 is planning to attend a service honoring the victims Thursday in Boston, where police were stationed on street corners across downtown and some residents admitted they were nervous moving about in public spaces.
People lined up hours ahead of time Thursday morning to get into the city's Roman Catholic cathedral for the interfaith service.
Massachusetts Gov. Deval Patrick said he shared the frustration that the person or people responsible were still at large, but he said solving the case will not "happen by magic."
"It's going to happen by doing the careful work that must be done in a thorough investigation," Patrick said. "That means going through the couple of blocks at the blast scene square inch by square inch and picking up pieces of evidence and following those trails, and that's going to take some time."
The bombs were crudely fashioned from ordinary kitchen pressure cookers packed with explosives, nails and ball bearings, investigators and others close to the case said. Investigators suspect the devices were then hidden in black duffel bags and left on the ground.
As a result, they were looking for images of someone lugging a dark, heavy bag. Investigators had appealed to the public to provide videos and photographs from the race finish line.