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 one behind the other in the crowd, and the one 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. Though it may be difficult, the nation is counting on those with information to come forward and provide it to us," DesLauriers said.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.