Investigators are appealing to the public to come forward with photos, videos, or any clues that could help solve the Boston Marathon bombings.
The FBI has circulated information about the bombs, which involved kitchen pressure cookers packed with explosives, nails and other lethal shrapnel — but authorities say so far nobody has claimed responsibility for Monday's attack.
At a news conference Tuesday the FBI said witnesses could have seen a bomber carrying an unusually heavy nylon bag, weighed down with shrapnel-packed explosives.
Investigators are combing surveillance tapes from businesses around the finish line and asking travelers at Logan Airport to share any photos or video that might help.
The bombings killed three people and injured more than 170.