Richard DesLauriers, the special agent in charge of the FBI's Boston field office, presented the media with images around 5 p.m. EDT Thursday of two men identified as suspects in Monday's Boston bombing that killed three people and maimed many others.
Since the explosions, FBI agents "developed a single person of interest" DesLauriers told a raucous crowd of reporters. Then agents worked to determine if the suspect acted alone, he said.
"Through the process the FBI developed a second suspect," DesLauriers added. "They appear to be associated."
Photos of the two men show that one was wearing a white baseball cap and another a black cap. The man with a white cap was videotaped placing a bag on the ground near one of the bomb sites.
The photos do not show a clear image of either man's face.
Video showed that the men "appear to be walking together ... in the direction of the finish line" before the attacks, the chief investigator said.
DesLauriers said the photos are the only ones the public should look at when considering suspects, in an apparent swipe at widespread crowdsourcing of photos in which users of Reddit, 4Chan and other websites searched for possible culprits.
Speculation about other suspects, he said, would "unnecessarily divert the public's attention."
"We are working methodically and with a sense of urgency," DesLauriers said. "We consider them to be armed and extremely dangerous."
Possible sightings of the suspects should be reported to 1-800-CALL-FBI.
Video Footage Released by FBI: