(CNN) — The FBI on Thursday released photos and video of two men it called suspects in the deadly bombings at the Boston Marathon and pleaded for public help in identifying them.
Within minutes, the photos were shared millions of times around the world.
The two men were photographed on Monday walking together near the finish line of the marathon before the explosions that killed three people and wounded about 180. One of the two men was seen setting down a backpack at the site of the second explosion “within minutes” of the blast, said Special Agent Rick DesLauriers, the head of the FBI’s Boston office.
“Somebody out there knows these individuals as friends, neighbors, co-workers or family members of the suspects,” DesLauriers said. “And though it may be difficult, the nation is counting on those with information to come forward and provide it to us.”
But he cautioned that the men should be considered armed and “extremely dangerous.”
“No one should approach them. No one should attempt to apprehend them except law enforcement,” he said.
DesLauriers said the FBI has been working on thousands of leads since Monday.
“We are working methodically and with a sense of urgency to identify those responsible for the bombings. Within the last day or so through that careful process we initially developed a single person of interest,” he said.
“Not knowing if the individual was acting alone or in concert with others, we obviously worked with extreme purpose to make that determination.”
The FBI said no other photos other than those provided on Thursday should be used to identify the suspects.
“Other photos should not be deemed credible and they unnecessarily divert the public’s attention in the wrong direction and create undue work for vital law enforcement resources,” DesLauriers said.
For information or to provide tips, go to fbi.gov, call 1-800-CALL-FBI.
The announcement capped a day in which President Barack Obama brought a mixture of reassurance and defiance to an interfaith memorial service in the city's Cathedral of the Holy Cross.
Whoever planted the bombs "picked the wrong city" to attack, he said.
Obama added, "Yes, we will find you. And yes, you will face justice. We will hold you accountable."