BOSTON, MA (RNN) - The FBI released images of two men they believe are responsible for the Boston Marathon bombings and asked for the public's help in positively identifying the suspects.
"At this time, these are the sole suspects we believe are responsible," said Richard DesLauriers, special agent in charge of the FBI Boston field office.
DesLauriers said video helped investigators pinpoint when and where the suspects planted bags they believed contained explosive devices.
The only one observed planting a device is the man the FBI identified as Suspect 2. He was wearing a white baseball cap and dark clothing.
Suspect 1 was wearing a dark cap, dark jacket and khaki pants.
President Barack Obama said the people of Boston had taught everyone to persevere and "push on" in the wake of the fatal marathon bombings.
"In the face of those who would visit death upon innocents, we will choose to save and comfort and heal," he said Thursday at an interfaith service.
The service was held at the Cathedral of the Holy Cross in tribute to the three who died and the 180-plus injured in the attack Monday. First lady Michelle Obama also joined her husband, city officials, state legislators and religious leaders in attendance.
Obama said everyone's prayers were with the families of those lost in the bombing. He recalled 8-year-old Martin Richard's circulated picture holding a sign reading, "No more hurting people" and "peace."
Also, he talked about Krystle Campbell, the 29-year-old woman that was killed.
"Our prayers are with the Campbell family of Medford – they're here today," Obama said. "Their daughter Krystle was always smiling."
Lu Lingzi, a Boston University graduate student and Chinese national, also died as a result of the bombing.
"Our prayers are with the Lu family of China who sent their daughter Lingzi to BU so she could experience all this city has to offer," Obama said.
Massachusetts Gov. Deval Patrick also spoke. He invoked the words of Martin Luther King Jr. to describe the response to the tragedy.
"In a dark hour, so many of you showed so many of us that darkness cannot drive out darkness, as Dr. King said," Patrick said. "Only light can do that."
Mayor Thomas Menino called his city a place with "courage, compassion and strength that knows no bounds."
"Nothing can defeat the heart of this city," he said. "Nothing will take us down because we take care of one another."
The FBI plans to have a news conference at 5 p.m. ET. Investigators have reviewed footage of the bombing and identified two possible suspects.
On Thursday, Secretary of Homeland Security Janet Napolitano spoke in front of the House Homeland Security Committee. She said video revealed individuals "the FBI would like to speak with" but would not call them suspects.
CNN reported a law enforcement source said two men had been identified as people of interest. One of them could be seen carrying a black backpack and the other a duffel bag, which the FBI said could have been used to carry the explosives.
Photos of the men have been distributed to law enforcement but will not be released to the public, according to CNN. The Boston Globe also stated officials had clear images of suspects, one at each bomb location, from video.
Boston City Council President Stephen Murphy told the Associated Press he had been briefed on the investigation by city police. He said video from a department store's security camera caught a man dropping off a bag near the blast site, and officials matched those findings with witness descriptions.
"[The investigation] is very active and very fluid right now," Murphy told AP. "They may be on the verge of arresting someone, and that's good."
The president issued an emergency declaration for Massachusetts. It authorized FEMA to provide assistance for emergency measures to save lives and to protect property, public health and safety.
The marathon, held annually on Patriots Day, brings tens of thousands of runners from around the world and hundreds of thousands of spectators. A pair of blasts within seconds of each other near the finish line of the race around 2:50 p.m. Monday killed three people and injured 183 others.
ABC News reported 63 of the injured remained hospitalized Wednesday night, including 12 in critical condition.
On Wednesday, Reuters released photos taken of the suspected explosive device's remains. Wiring, a circuit board and remnants of a pressure cooker could be seen in the images.
Other things shown included metal BBs fused together, nails, various pieces of unidentified metal, black nylon from a duffel bag and batteries.
Authorities also found the lid to the pressure cooker on the roof of a building near the blast site.
A Boston federal courthouse was cleared out Wednesday for a bomb scare after throngs of people showed up. The crowds formed after widespread reports of a bombing suspect in custody, which were later refuted by the Justice Department, FBI and city police.
Patrick declined comment Wednesday when asked if the FBI had a suspect's name. He told CNN there had been a lot of misinformation going around, but the investigation was making progress.
"[Investigators] are doing this in a very methodical way, a very thorough way," Patrick said. "It is several blocks over there they are covering a square inch at a time and piecing the story together."
Police ask anyone with information to call 1-800-494-TIPS. Anyone looking for information on loved ones can call 617-635-4500.