A photo released by the FBI shows both Boston bombing...

A photo released by the FBI shows both Boston bombing suspects together. Authorities say the suspect pictured here wearing a black hat was killed in a shootout with police on April 18, 2013. Credit: FBI

The FBI Thursday released video images of two suspects caught on tape near the site of the Boston Marathon bombings, with authorities saying one of them -- a young man in a white baseball cap sitting backward on his head -- left a dark-colored backpack where the second device exploded.

That man, "suspect number two," placed the pack in front of the Forum restaurant, at 755 Bolyston St., FBI Special Agent in Charge Richard DesLauriers said at an afternoon news conference. He appealed to the public to help identity the two men.

The images show the pair walking, one in front of the other, through the marathon crowd. The first man is in a dark baseball cap and a nylon coat with a white T-shirt underneath, the backpack draped over both shoulders. The second man in the white backward cap is wearing a light jacket, with his backpack slung over his right shoulder.

"As you can see, the quality of the photos is quite good," DesLauriers said. He said all other images -- including those published by major news outlets on Thursday -- are not credible. "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."

He said "each piece moves us forward to justice," and strongly urged the public not to approach the men. "We consider them to be armed and extremely dangerous," he said. "Do not take any action on your own."

Sources told Newsday that the two men were singled out because of their demeanor, reaction to the blasts and their backpacks, deemed similar to the ones authorities believe were used to hold two pressure cookers stuffed with nails and ball bearings. The sources said they believe the men may have been working together, because it would have been difficult for one person to carry both bombs.

The sources said authorities have seen this sort of "drop and walk" method of planting bombs in crowded places like marketplaces in Iraq, Afghanistan and Israel. This method has also been taught by al-Qaida and other terror groups in its propaganda, sources said.

The sources also said that the FBI has set up a command post along Boston Harbor where it is analyzing more than 300 pieces of evidence and using facial recognition software to help identify people seen in marathon footage. Also, investigators in white jump suits entered the sewers along the parade route, sifting through potential evidence.

Three people were killed in the blasts, including Martin Richard, 8; Krystle Campbell, 29, a restaurant manager; and Lu Lingzi, 23, a Boston University graduate student from China. More than 170 were injured, many critically.

Before the release of the video images, President Barack Obama spoke at an interfaith service at Boston's soaring Cathedral of Holy Cross. As for the perpetrators, he told the packed cathedral, "We will find you. We will hold you accountable. But more than that, our fidelity to our way of life -- to our free and open society -- will only grow stronger. For God has not given us a spirit of fear and timidity but one of power and love and self-discipline."

As the city continued to deal with the marathon tragedy, many survivors continued to make progress in area hospitals. The youngest victim, a 5-year-old, is improving after suffering life-threatening injuries, doctors said.

"I think he's gonna be OK, and that's great," said Peter Burke, Boston Medical Center's chief of trauma services, at a news conference. He said the child is no longer in critical condition. The boy's mother was also hurt.

Doctors said the wounds they have treated in the bombings are comparable to those suffered by soldiers serving in Iraq and Afghanistan.

"Over the last few days, there were a fair amount of questions and some interest in how this experience compared to a wartime experience," said Joseph Blansfield, the Trauma Program manager at the hospital, who also treated battlefield injuries in Iraq. "This was disturbingly similar to our experiences with improvised explosive devices and treating large numbers of traumatized individuals."

Surgeons at Boston Medical have amputated seven limbs on five patients, officials said.

Sixteen patients remain at the hospital, including 10 in serious condition and five in fair condition. A 60-year old man remains in critical condition, Burke said.

Brigham and Women's Hospital treated 35 people hurt in the blasts. Of those, 10 remain in the hospital, with three in critical condition.

Twelve patients are still being treated at Beth Israel Deaconess Medical Center. Only one remains in the intensive care unit; that patient is in serious condition. All others are in good or fair condition, a spokeswoman said.

The facility conducted three leg amputations on three patients.

As Boston presses on, New Yorkers have come to lend a hand. NYPD Officer Joe Rao, of Bay Shore, said he and other cops from Long Island were eager to assist.

They spent the day handing out water and snacks to first responders, law enforcement and the public.

"Long Islanders want to help," he said. "We're doing everything we can. We didn't forget the way Boston police rushed to New York when we needed them. We'll be here as long as they need us. Whatever it takes."

Anne Boyle, a Bostonian whose friend was hurt in the bombings while watching the race, said she was moved by the presence of the New York City police.

"They're the ones who understand what we're going through, because they lost so many of their friends on 9/11." she said. "Seeing them here is good for us. It helps."

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