BOSTON (Reuters) - President Barack Obama was due to visit Boston on Thursday to attend a 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.
Obama will address an interfaith service and by extension the country following the blasts that killed three people and wounded 176 in the worst attack on U.S. soil since September 11, 2001. No arrests have yet been made in the investigation.
A line of people several city blocks long formed outside the Cathedral of the Holy Cross in Boston's South End, about a mile from the bombing site.
"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."
Security was heavy around the church, with dozens of city police officers and bomb-sniffing dogs. Police were also out in force around the bombing site, which remains closed off for several blocks as they search for evidence.
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 are also due to 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 September 11 suicide hijackings 12 years ago.
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.
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 September 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."
(Editing by Daniel Trotta, Lisa Von Ahn and Lisa Shumaker)