BREAKING: Feds release photos, video of Boston bombing suspects

BOSTON (AP) — 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.

The photos depict one man in a dark baseball

cap and the other in a white cap worn backward. The men were seen

walking together

in the crowd, and the one in the white hat was seen setting down a

backpack at the site of one 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.

Though it

may be difficult, the nation is counting on those with information

to come forward and provide it to us," 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 two men — dubbed Suspect 1 (in the dark

hat) and Suspect 2 (in the white hat) — 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.

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. FBI photo-analysis

specialists have been analyzing a mountain of surveillance footage

and amateur pictures and video for clues to who carried the attack

and why.

Generally, law enforcement agencies release photos of suspects only as a last resort, when they need the public's help in

identifying or capturing someone.

Releasing photos can be a mixed bag: It can tip off a suspect and deny police the element of surprise. It can also trigger

an avalanche of tips, forcing police to waste valuable time chasing them down.

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.

"When you have something that is this high-profile, they are going to use every available resource that they have," said former

Miami federal prosecutor Melissa Damian Visconti.

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.

But after years of investigating terrorist incidents and other crimes, the FBI is practiced at cataloging, categorizing and

analyzing such evidence and will winnow it down dramatically, he said.

"Back in the days of 20 years ago, you were lucky if you had video and it was probably of poor quality and it took a tremendous

amount of enhancement. Today you have a completely different issue," Grindstaff said.

Investigators can set the video analysis

software so that it automatically searches for certain types of objects

or people

matching a height and weight description. The software can also

spot patterns that analysts might not notice, such as a certain

car that turns up in different places, Grindstaff said.

DiZinno, who ran the FBI lab from 2007 to 2010, said any retrieved bomb components such as the pressure cookers, shrapnel

and pieces of timers or wire will be closely examined for fingerprints, DNA, hairs and fibers.

The bomb components would be traced by

figuring out the item's maker, where each piece is typically purchased

and whether

the device resembles any bombs the FBI has seen in past attacks.

The FBI lab keeps a detailed file on past bombings, including

many overseas attacks.

"Let's say there was a timer," DiZinno said. "Was there a serial number? Who was the manufacturer? That can provide leads

for investigators."

One pressure cooker maker, the Fagor Group

in Spain, said that it has been contacted by U.S. investigators and that

company

officials are extending full cooperation. The company sells

250,000 pressure cookers a year in the U.S. and 1 million worldwide.