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.
Boston remained under a heavy security presence, with scores of National Guard troops gathering among armored Humvees in the Boston Common.
Kenya Nadry, a website designer, took her 5-year-old nephew to a playground.
"There's still some sense of fear, but I feel like Boston's resilient," she said. "The fine men in blue will take care of a lot of it."
Dr. Horacio Hojman, associate chief of trauma at Tufts Medical Center, said patients were in surprisingly good spirits when they were brought in.
"Despite what they witnessed, despite what they suffered, despite many of them having life-threatening injuries, their spirits were not broken," he said. "And I think that should probably be the message for all of us — that this horrible act of terror will not bring us down."
Obama and his challenger in the last election, former Massachusetts Gov. Mitt Romney, planned to visit Boston on Thursday to attend the vigil.
The blasts killed 8-year-old Martin Richard, of Boston, 29-year-old Krystle Campbell, of Medford, and Lu Lingzi, a Boston University graduate student from China.
- Marathons to Rethink Security in Wake of Boston
- Social Media Reacts to First Reports of Explosion
- Opinion: My Boston
Associated Press writers Jay Lindsay, Pat Eaton-Robb, Steve LeBlanc, Bridget Murphy and Meghan Barr in Boston; Eileen Sullivan, Julie Pace and Lara Jakes in Washington; and Marilynn Marchione in Milwaukee contributed to this report.