BOSTON — The FBI Thursday released video clips and photos of two nameless "armed and extremely dangerous" suspects in the Boston Marathon bombings and asked for the public's help in identifying them.
"Somebody out there knows these individuals," said Boston FBI Special Agent Richard DesLauriers. "Thought it may be difficult, the nation is counting on those with information to come forward and provide it to us."
The images show two men in baseball caps, one of whom is seen putting down a black backpack at the second blast site. Both were seen walking together through the crowd of spectators.
"We consider them to be armed and extremely dangerous," said DesLauriers. "No one should approach them. If you see these men, contact law enforcement."
Investigators said the suspects images came from a surveillance camera in the finish-line area of the marathon. Investigators have spent hours poring over video, frame by frame, since the bombings Monday at 2:50 p.m. that killed three and injured 175, many severely.
In Washington earlier in the day, Homeland Security Secretary Janet Napolitano told a congressional committee "we need the public's help in locating these individuals." She also said it is too soon to say if the Boston bombings are connected to a domestic or foreign terrorist plot.
"This is not an NCIS episode," she said. "Sometimes you have to take time to properly put the chain together to identiy the perpetrators, but everybody's committed to seeing that that gets done in the right way."
President Obama, who called the bombings an act of terrorism, and his wife, Michelle, attended an interfaith hearling service Thursday at Boston's Cathedral of the Holy Cross. The pews in the front of the church were filled with family and friends of the victims.