The painstaking work to identify the bombing suspects from reams of Boston Marathon footage yielded a possible breakthrough as investigators focused on a man seen dropping off a bag, and then walking away from the site of the second of two deadly explosions.

In a press conference on Thursday, FBI Special Agent Richard DesLauriers said two suspects are now sought in the investigation.

The FBI has released photos and are listing the public's help to identify the suspects who appear to be associated, officials said.

The first suspect wore a white hat, and the second suspect was wearing a dark hat, officials said. The suspects were seen walking around on Boylston Street.

"The only one observed to be planting a device was suspect number two in a white cap," said DesLauriers.

Surveillance video released to the media shows two men walking together, one walking in front of the other, with the man in the white hat wearing a backpack.

The discovery of the images - found on surveillance footage from a department store near the finish line - emerged two days after the attack that left three people dead, wounded more than 170, and cast a dark shadow over one of this city's most joyous traditions. The footage hasn't been made public.

Massachusetts Gov. Deval Patrick said he shared the frustration that the person or people responsible were still at large, but he said solving the case will not "happen by magic."

"It's going to happen by doing the careful work that must be done in a thorough investigation," Patrick said. "That means going through the couple of blocks at the blast scene square inch by square inch and picking up pieces of evidence and following those trails, and that's going to take some time."

The bombs were crudely fashioned from ordinary kitchen pressure cookers packed with explosives, nails and ball bearings, investigators and others close to the case said. Investigators suspect the devices were then hidden in black duffel bags and left on the ground.

As a result, they were looking for images of someone lugging a dark, heavy bag. Investigators had appealed to the public to provide videos and photographs from the race finish line.

City Council President Stephen Murphy, who said he was briefed by Boston police, said investigators saw the image of the man dropping off a bag and matched the findings with witness descriptions of someone leaving the scene.

One department store video "has confirmed that a suspect is seen dropping a bag near the point of the second explosion and heading off," Murphy said.

Separately, a law enforcement official who was not authorized to discuss the case publicly and spoke to The Associated Press on the condition of anonymity confirmed only that investigators had an image of a potential suspect whose name was not known to them and who had not been questioned. The official said investigators did not know the man's name.

Several media outlets reported that a suspect had been identified from surveillance video taken at a Lord & Taylor department store between the sites of the bomb blasts.

At least 14 bombing victims, including three children, remained in critical condition. Dozens of victims have been released from hospitals, and officials at three hospitals that treated some of the most seriously injured said they expected all their remaining patients to survive. A 2-year-old boy with a head injury was improving and might go home Thursday, Boston Children's Hospital said.

On Wednesday, investigators in white jumpsuits fanned out across the streets, rooftops and awnings around the blast site in search of clues. They picked through trash cans, plastic cup sleeves and discarded sports drink dispensers.

Marian Wilson said she tried not to notice the men slowly pacing and looking for evidence on the street behind her as she ate a tuna sandwich at Stephanie's on Newbury, a restaurant a block from the site of the bombings.

"I just go in and out of being completely freaked out," she said.

Full Text: FBI update on Boston Marathon bombings

Good afternoon. My name is Richard DesLauriers. I am the special agent in charge of the Boston Division of the FBI.

Since Monday’s bombings, the FBI and our law enforcement partners have been working around the clock and are fully committed to investigating this matter to bring those responsible for justice.

Our collective law enforcement team has pursued thousands leads and tips. As I said two days ago, 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. Not knowing if the individual was acting alone or in concert with others, we obviously worked with extreme purpose to make that determination. The entire force of the federal government, the FBI in Boston and around the world, as well as our partners in the Boston Police, ATF, Massachusetts State Police, and the more than 30 agencies of the Joint Terrorism Task Force, have set about to ensure that all responsible for the bombings will be brought to justice.

More importantly, it was done to ensure the future safety of the city, the commonwealth and the country. Indeed, through that process, the FBI developed a second suspect.

Today, we are enlisting the public’s help to identify the two suspects.

After a very detailed analysis of photo, video, and other evidence, we are releasing photos of the two suspects. They are identified as Suspect 1 and Suspect 2. They appear to be associated.

Suspect 1 is wearing a black hat

Suspect 2 is wearing a white hat.

Suspect 2 set down a back pack at the site of the second explosion just in front of the Forum Restaurant.

We strongly encourage those who were at the Forum Restaurant who have not contacted us yet to do so.

As you can see from one of the images, Suspects 1 and 2 appear to be walking together through the marathon crowd on Boylston Street in the direction of the finish line. That image was captured as they walked on Boylston in the vicinity of its intersection with Gloucester Street.
As you can see, the quality of the photos is quite good, but we will continue to work on developing additional images to improve their identification.

Further, on FBI.gov, we have videos of the suspects. The photos and videos are posted for the public and media to use, review and publicize.
For clarity, these images should be the only ones—the only ones—that the public should view to assist us. Other photos should not be deemed credible and unnecessarily divert the public’s attention in the wrong direction and create undue work for vital law enforcement resources.

For more than 100 years, the FBI has relied on the public to be its eyes and ears. With the media’s help, in an instant, these images will be delivered directly into the hands of millions around the world. We know the public will play a critical role in identifying and locating them.

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.

No bit of information, no matter how small or seemingly inconsequential, is too small. Each piece moves us forward towards justice.

It is extremely important to contact us with any information regarding the identities of Suspect 1 and Suspect 2 and their locations.

We considered them to be armed and extremely dangerous. No one should approach them. No one should attempt to apprehend them except law enforcement. Let me reiterate that caution. Do not take any action on your own. If you see these men, contact law enforcement. If you know anything about the bombings or the men pictured here, please call the telephone listed on the photo arrays—that’s 1-800 CALL FBI. Again that’s 1-800 225-5324. All calls will be kept confidential.

We also have established a website for tips that directly relate to the bombing—bostonmarathontips.fbi.gov. Again, that website is bostonmarathontips.fbi.gov

The photos can be viewed on our website: FBI.gov.

The images from Monday are indelible and the horror of that day will remain with us forever. This further underscores our obligation to investigate this crime judiciously in order to bring those responsible to justice. The victims and the survivors deserve that much.

As to Monday’s victims, the FBI is committed to ensuring that victims receive the rights they are entitled to and the assistance they need to cope with crime. Treating victims with respect and providing them with assistance benefits victims and helps us build better cases. Our resources include an Office for Victim Assistance at FBI Headquarters and victim specialists nationwide. These highly trained professionals can assist victims and coordinate with other agencies to provide victims with the support, information, and resources necessary to effectively meet their needs. Our victim specialist team continues to work around the clock to bring assistance to the victims of this heinous act.

Identifying and locating those responsible is now our priority. No other details of the investigation will be released at this time because this is our focus now.

Review these photographs and contact us at 1-800-CALL-FBI or bostonmarathontips.fbi.gov immediately.

Thank you.