NY TIMES
Officials said they have images of one of the men putting a black backpack on the ground just minutes before two near-simultaneous blasts went off near the finish line of the marathon at 2:50 p.m. on Monday. One video, which officials said they did not release, shows the two men walking slowly away after a bomb exploded while the crowd fled.
At a news briefing here, Richard DesLauriers, the special agent in charge of the F.B.I.’s Boston field office, initiated the unprecedented crowd-sourcing manhunt by urging the public to look at the pictures and video on the F.B.I.’s Web site, fbi.gov. The two men appear to be in their 20s, but Mr. DesLauriers did not characterize their appearance or offer an opinion as to their possible ethnicity or national origin.
“Somebody out there knows these individuals as friends, neighbors, co-workers, or family members of the suspects,” Mr. DesLauriers said firmly and grimly into the cameras. “Though it may be difficult, the nation is counting on those with information to come forward and provide it to us.”
Michael R. Bouchard, a former assistant director of the Bureau of Alcohol, Tobacco, Firearms and Explosives, said that in releasing the pictures and video, the authorities took a calculated risk.
“If you don’t release the photos, the bad guys don’t know you’re on to them while you’re looking,” said Mr. Bouchard, who helped oversee the Washington-area sniper case in 2002 and now runs his own security firm in Vienna, Va. “If you do release them, you run the risk they see them and change their appearance or go underground. The authorities made a calculated decision the benefits of releasing the photos outweighed the risks of holding back and trying to identify them themselves.”
They don’t know if these guys are from out of town, so they had to cast their net wider,” said Mr. Bouchard, who said the widespread use of social media and cellphones make such identifications easier than just a few years ago.
At the briefing, Mr. DesLauriers did not specify what led the F.B.I. to call the two men suspects, but he said that the decision was “based on what they do in the rest of the video.” According to officials, when the blasts went off, most people fled in panic, but these two did not and instead walked away slowly, almost casually.
“We have a lot more video than what we released,” the official said. “The sole purpose of what we released was to show the public what they looked like.”
The fact that F.B.I. officials chose to make the video images public suggested to some people familiar with law enforcement tactics that they have not been able to match them with faces in government photo databases, said Jim Albers, senior vice president at MorphoTrust USA, which supplies facial recognition technology to the United States. The F.B.I. has a collection of mug shots of more than 12 million people, mostly arrest photos.
That could be a question of the quality of the images of the two suspects — the video clips posted by the bureau do not include high-resolution frontal images of the two men’s faces, as would be ideal for facial recognition software, Mr. Albers said. Or it may be that the search software, which produces a list of matches ranked by probability, simply did not find a persuasive match.
