The FBI previously asked the thousands of people who congregated near the finish line to submit photos and video taken at the crime scene. That combined with media coverage of the marathon and surveillance cameras gave investigators an abundance of images to review.
The team discovered the first suspect "within the last day or so," DesLauriers told a news conference. That enabled them to connect him to the second man.
"Somebody out there knows these individuals as friends, neighbors, co-workers or family members of the suspects," DesLauriers said, while cautioning people that the men were considered armed and extremely dangerous.
A law enforcement official familiar with the investigation said that at various times over the last few days investigators thought they might have identified the men in the pictures. But all the tentative identifications proved uncorroborated, which is why the FBI decided to make the images public.
Investigators hoped the men would be identifiable within hours of the release of the pictures and video, a national security official said, also 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.