Federal investigators said Wednesday they are working to identify a person in a video who appeared to leave a bag in the spot where one of two bombs later exploded near the finish line of the Boston Marathon.
Authorities also are trying to identify at least one other person seen in videos of the crowd, according to people familiar with the matter.
The new information emerged on a day of roller-coaster emotions in the city where three were killed and more than 175 injured Monday. Several news organizations reported that a suspect was in custody and would be transported to the federal courthouse in Boston, prompting crowds to gather there, but authorities later said no arrest had been made.
The quest to tease useful information from a mountain of evidence, including what one lawmaker called the equivalent of hundreds of hours of video, bore its first fruit with the images of the suspicious person near the marathon's finish line.
Investigators pored over surveillance video from retail stores and restaurants near the bombing site as well as video and photographs from citizens, news organizations and other sources, officials said.
The officials stopped short of calling the person with the bag a formal suspect in the attack, after past cases where initial investigative targets turned out to be innocent.
The two explosives were placed in black bags or backpacks, the Federal Bureau of Investigation has said, and officials said the bag seen in the video seemed to be made from material similar to the shreds of black nylon found at the bombing site.
