Word of a break in the story caused about 120 reporters and photographers to hurry to a Sheraton hotel - not far from the marathon finish line - for the 5 p.m. FBI briefing. Bomb-sniffing dogs outside a third-floor ballroom checked everyone's bags. Journalist and officials barely fit in the ballroom, along with two dozen television cameras.
Still images were displayed on two large black easels. One poster showed four images of the suspect with the black cap and the other displayed four of the suspect in the white cap.
While the still and video images were slightly blurred, experts said they will help investigators determine the height, weight and body types of the suspects.
Michael Bouchard, a former assistant director of the the Bureau of Alcohol, Tobacco, Firearms and Explosives, said investigators probably weighed the consequences of releasing the images. On the one hand, the disclosure could force the suspects to try to change their appearances and disappear, he said. On the other hand, distributing the images worldwide could lead to their identification and capture soon.
"They had to weigh the risk," said Bouchard, who led the investigation of the District of Columbia sniper case in 2002 and is president of Security Dynamics, a consulting firm. "Someone has seen them in their neighborhood. They have a higher likelihood of solving this quickly based on these images."
He also said investigators are probably hoping that the pictures will jar the memories of people who might have encountered the suspects along the race course.
Earlier Thursday, President Barack Obama eulogized the three young victims of the bombings and offered encouragement to the scores of people injured in the attacks, telling a packed cathedral in the city's South End that "Boston's your home town, but we claim it a little bit, too."
"Every third Monday in April, you welcome people from all around the world to the Hub - for friendship and fellowship and healthy competition," Obama said during an interfaith service of healing held at the soaring Cathedral of the Holy Cross. "A gathering of men and women of every race and every religion, every shape and every size, a multitude represented by all those flags that flew over the finish line."
Bringing the crowd to its feet, the president said that the marathon held in Boston every year for well over a century exemplified the very best of the city and the nation, a resilience and determination he characterized as the ability to "finish the race."
"Even when our heart aches, we summon the strength that maybe we didn't even know we had. We finish the race," Obama said. "And this time next year, on the third Monday in April, the world will return to this city and run harder than ever, and cheer louder than ever, for the 118th Boston Marathon. Bet on it."
Obama mourned the three people killed in the bombings: Martin Richard, an 8-year-old from the Dorchester, Mass. neighborhood of Boston; Lu Lingzi a 23-year-old graduate student from China; and Krystle Campbell, a 29-year-old restaurant manager from Medford, Mass.
Following the service, Obama went to nearby Cathedral High School, where he addressed hundreds of marathon volunteers and officials of the Boston Athletic Association, which organizes the marathon. The main message, Obama said, was "to say how proud the whole country is of you."
He next went to Massachusetts General Hospital, where he met with medical staff and patients injured in the bombings. Obama's words to the patients in their hospital beds were private. But he gave a sense when he addressed their absence at the church: "Know this: As you begin this long journey of recovery, your city is with you. Your commonwealth is with you. Your country is with you. We will all be with you as you learn to stand and walk and, yes, run again. Of that I have no doubt. You will run again."