The FBI released photos and video Thursday of two suspects in the Boston Marathon bombing and asked for the public's help in identifying them, zeroing in on the two men on surveillance-camera footage less than three days after the deadly attack.
FBI agent Richard DesLauriers said the photos of the two men came from surveillance cameras near the explosion sites. One man is seen wearing a dark baseball cap, the other a white cap worn backwards.
The man in the white cap is seen setting down a backpack at the site of one of the blasts, DesLauriers said.
Within moments of the announcement, the FBI website crashed, perhaps because of a crush of visitors.
The images were released hours after President Barack Obama and first lady Michelle Obama attended an interfaith service at a Roman Catholic cathedral in Boston to remember the three people killed and more than 180 wounded in the twin blasts Monday at the marathon finish line.
The break in the investigation came just days after the attack that tore off limbs, shattered windows and raised the specter of another terrorist attack on U.S. soil.
The suspects are considered armed and extremely dangerous, DesLauriers said, and people who see them should not approach them.
"Do not take any action on your own," he warned.
At the Cathedral of the Holy Cross earlier in the day, Obama declared to the people of Boston: "Your resolve is the greatest rebuke to whoever committed this heinous act." He spoke in almost mocking terms of those who commit such violence.
"We finish the race, and we do that because of who we are," the president said to applause. "And that's what the perpetrators of such senseless violence - these small, stunted individuals who would destroy instead of build and think somehow that makes them important - that's what they don't understand."
"We will find you," he warned those behind the attack.
Seven victims remained in critical condition. Killed were 8-year-old Martin Richard of Boston, 29-year-old restaurant manager Krystle Campbell of Medford, Mass., and Lu Lingzi, a 23-year-old Boston University graduate student from China.
Video and photos recovered in the investigation are being examined and enhanced by an FBI unit called the Operational Technologies Division, said Joe DiZinno, former director of the FBI lab in Quantico, Va.
Investigators are looking at video frame by frame - a laborious process, though one aided by far more sophisticated facial recognition technology than is commercially available, forensic specialists said.
The investigation will probably collect about a million hours of videotape from fixed security cameras and cellphones and cameras used by spectators, said Gene Grindstaff, a scientist at Intergraph Corp., a Huntsville, Ala., company that makes video analysis software used by the FBI and other law enforcement agencies.
(Copyright 2013 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.)
On mobile? Copy this link to view the video: http://bit.ly/Yy9gIS
7831 N. Business Park Drive