Obama Visits Boston Amid Search for Marathon Bombing Suspect Seen on Video

WATCH LIVE: U.S. president addressed interfaith service, and by extension the country, following blasts that killed three people and wounded 176 in the worst attack on U.S. soil since Sept. 11, 2001. No arrests have yet been made in attack.

U.S. President Barack Obama vowed Thursday to bring the perpetrators of  Boston Marathon bombings to justice, and pledged that the city would overcome Monday's attack. 

Obama spoke at an interfaith memorial service for victims of the Boston Marathon bombing amid a manhunt for a suspect seen on video taken before two blasts struck near the finish line on Monday. Three people were killed people and 176 wounded in the attack, which was the worst on U.S. soil since September 11, 2001. No arrests have yet been made in the investigation.

"For millions of us, what happened on Monday is personal," the president said.

Obama vowed that justice will come to the perpetrator of the bombings and stressed that the city would not be defeated by the terrorist attack. "Yes, we will find you and you will face justice," Obama pledged.

Like a runner that has been kicked off his feet, Obama vowed that the city would "finish the race." Addressing the runners wounded in the blast, Obama said: "I have no doubt you will run again. Your resolve is the greatest rebuke to whoever committed this act."

"This time next year, on the third Monday in April, the world will return to this American city to run harder than ever and cheer even louder for the 118th Boston Marathon. Bet on it," Obama said to thunderous applause. 

Hundreds of people crowded outside the cathedral in Boston's South End, about a mile from the bombing site, before the service.

"President Obama knows how important the city of Boston is to the nation and the world," said 55-year-old John Snyder, who had joined the line before sunrise. "He is bringing his light to us for much-needed healing."

Dozens of uniformed police officers in bright yellow vests formed a security line around the church. City officials used buses to block access to nearby cross streets.

Boston Mayor Tom Menino, who has been making public appearances in a wheelchair since breaking a bone in his leg over the weekend; Massachusetts Governor Deval Patrick; and Cardinal Sean O'Malley will also speak at the service.

The service comes the day after the FBI arrested a Mississippi man in connection with letters believed to have contained the deadly poison ricin and sent to federal officials, including Obama. In a separate incident on Wednesday, an explosion at a Texas fertilizer plant killed as many as 15 people.

The FBI said there was no indication of a connection between the ricin letters and the Boston bomb attacks, but they reminded Americans of anthrax mail attacks in the wake of the Sept. 11 suicide hijackings 12 years ago.

'All hands on deck'

U.S. Homeland Security Secretary Janet Napolitano said on Thursday that authorities had stepped up security at airports, transportation hubs and other sites around the county and that the investigation was moving forward.

"This is an all-hands-on-deck effort by the entire federal government, led by the president," Napolitano said in Congressional testimony. "We are committed to bringing the perpetrators to justice."

Investigators believe the Boston bombs were fashioned out of pressure cookers and packed with shrapnel. Ten victims lost limbs, and emergency room doctors reported plucking nails and ball bearing from the wounded.

The suspect in the video had not been identified by name, two U.S. government officials said.

Police had considered making an appeal to the public for more information at a news conference on Wednesday, a U.S. government source said, but the FBI canceled it after a number of delays.

The bombs in Boston killed an 8-year-old boy, Martin Richard; a 29-year-old woman, Krystle Campbell; and a Boston University graduate student and Chinese citizen, Lu Lingzi.

Video search

Ahead of his visit, Obama declared a state of emergency in Massachusetts, a move that makes federal funding available to the state as it copes with the aftermath of the bombing.

The crowded scene along the race course in central Boston on Monday was recorded by surveillance cameras and media outlets, providing investigators with significant video footage of the area before and after the two blasts.

Based on the shards of metal, fabric, wires and a battery recovered at the scene, the focus turned to whoever may have placed homemade bombs in pressure cooker pots and taken them in heavy black nylon bags to the finish line of the world-famous race.

Amid an outpouring of public support for the victims, Kenneth Feinberg, the attorney who oversaw compensation for victims of the Sept. 11 attacks and the April 2007 Virginia Tech shootings, was named to administer a fund for those affected by the Boston bombing.

The One Fund Boston, unveiled on Tuesday, was seeded with a $1 million donation from financial services firm John Hancock.

The fund was up to $7 million on Wednesday, its sponsors said, including donations from more than 8,500 people.

Tens of thousands of people turn out to watch and run in the marathon, which comes on a state holiday and is one of New England's best-attended sporting events.

"The president being here shows a sign of unity," said Mary Fitzgerald as she waited in line. "It makes me feel like he cares what happens to us."