Investigators released pictures of two suspects in the Boston bombing on Thursday (April 18), seeking the public's help in finding two men photographed on the crowded sidewalk before Monday's bombs exploded near the finish line.

Both men carried backpacks that were believed to contain the bombs. The man identified as suspect No. 1, who is now reported as dead wore a dark baseball cap. Suspect No. 2 wore a white cap backwards and was seen setting down his backpack on the ground.

Investigators hoped the men would be identifiable within hours of the release of the pictures and video, a national security official said, speaking on condition of anonymity.

Investigators were looking at the men for some period of time before deciding to make the videos public, and they had extensive video and still pictures to justify the FBI decision to label the two men as suspects, the official said.

At least one other person of interest who featured in crime scene pictures had been ruled out as a suspect. Also ruled out earlier in the week was a Saudi student who was injured in the attacks, the official said.

Presented by Adam Justice