Updated 10:10 PM ET
BOSTON Plucking a couple of faces in baseball caps out of a swarming crowd, the FBI zeroed in on two suspects in the Boston Marathon bombing and shared surveillance-camera images of them with the world Thursday in hopes the public will help hunt them down.
The somewhat blurry but still detailed photos and video depict one young man in a dark cap and another in a white cap worn backward, both wearing backpacks and one walking behind the other on the sidewalk near the finish line as marathoners run by.
The man in the white hat was seen setting down a backpack at the site of the second explosion, said Richard DesLauriers, FBI agent in charge in Boston.
"Somebody out there knows these individuals as friends, neighbors, co-workers or family members of the suspects," he said. "Though it may be difficult, the nation is counting on those with information to come forward and provide it to us."
They looked much like typical college students, but DesLauriers described them as armed and extremely dangerous, and urged anyone who sees or knows them to tell law enforcement and "do not take any action on your own."
The photos of the suspects can be seen online on fbi.gov. Any tips regarding the suspects can be called into the FBI at 1-800-CALL-FBI or send via the Web at bostonmarathontips.fbi.gov. Sources say investigators have leads on possible names, CBS News correspondent Bob Orr reported, but DesLauriers said the FBI still needs help.
CBS News has learned that FBI is reporting record traffic on its web sites as people go online to view stills and video of the suspected Boston bombers. The FBI is also getting an extremely high number of phone calls and emails.
Authorities believe both baseball caps have logos that are Bridgestone Golf.
Investigators had been focusing on a man wearing a white baseball cap seen dropping off a bag, and then walking away from the site of the second of two deadly explosions. Orr reported that investigators were able to retrace his steps and discovered video of the man with another man carrying a backpack.
The surveillance footage was released three days after the attack that left three people dead, wounded more than 170, and cast a dark shadow over one of this city's most joyous traditions.
Orr reported that after releasing the video, the FBI is hoping for tips that will identify the suspects. Investigators are using facial recognition software; scouring criminal databases; and trying to to find a match. They have some potential names for these suspects but they are currently unable to match.
As for whether this was an act of either foreign or domestic terrorism, Orr posed that question to a senior federal official, who said right now they think they are leaning-- and he emphasizes they don't have a definite-- that they are leaning more towards a domestic attack.
The FBI video is a compilation of segments, altogether about 30 seconds long. The planting of the backpack, as described by authorities, was not part of the footage made public.
CBS News correspondent John Miller explained why these two people are believed by the FBI to be possible suspects: "They have other video, including the one Orr referenced, where they believe they actually have on tape one of the suspects in the white baseball cap putting the bomb down in front of the Starbucks at the second location. But reason they selected the pictures we're seeing here is they wanted to find the pictures that didn't have the most sinister activity but the pictures that gave people the best chance of recognizing them."
The man in the dark hat was dubbed Suspect 1 by the FBI and appeared to be wearing sunglasses. The other, in the white hat, was labeled Suspect 2. Both appeared to be wearing dark jackets. The FBI did not comment on the men's height, weight or age range and would not discuss their ethnicity.
"It would be inappropriate to comment on the ethnicity of the men because it could lead people down the wrong path potentially," said FBI agent Greg Comcowich, a spokesman for the Boston FBI office.
The enlarged pictures of white-hatted Suspect 2 in profile and head-on were blurry but still remarkable in their detail and more revealing than those of Suspect 1.
While authorities said the information on the men began coming together over the previous day or so, agent Daniel Curtin said the FBI did not release the photos earlier because "it's important to get it right."
Distribution of the images brought both encouragement and unease to some Bostonians.
Jennifer Lauro of Topsfield, Mass., worried that the photos might breed fear and suspicion.
"It just looks like a college kid, so I think that's going to make people feel vulnerable," she said. "Because it could be anybody. It looks like any kid from Boston College or Boston University or any other school."