Those killed include 8-year-old Martin Richard, a resident of the city's Dorchester neighborhood whom babysitter Caitlin Doyle recalled as "just all-around a wonderful kid (with) a big, bright smile that no one could ever forget."
There was 29-year-old Krystle Campbell, who was "fun, outgoing (and) always there to help somebody," her grandmother Lillian Campbell said.
Lastly, there was the Boston University graduate student from China -- whom the school and Chinese consulate declined to identify by name. According to a LinkedIn profile, she graduated from a Chinese university with a degree in international economics and was set to earn her master's degree in mathematics and statistics in 2014 from B.U.
Others survived, thanks largely to the work of emergency personnel and volunteers on-site and scores of professionals in several world-class hospitals nearby.
Doctors removed more than a dozen nails from one patient, and three had been struck with metal beads slightly larger than BBs, said Dr. Ron Walls, the emergency medicine chairman at Brigham and Women's Hospital.
Back in Copley Square, in the heart of Boston, investigators on Tuesday continued searching for any hint that might lead them to the perpetrator.
Authorities also pleaded for the public's help. Did they know of anyone who made a threat involving April 15 or the marathon? Did they hear explosions in a remote area, possibly as a test run? And did they spot anyone near the finish line dropping off what ended up being the two bombs?
By 5 p.m. Tuesday, the FBI had gotten more than 2,000 tips, DesLauriers said. They'd also begun poring over scores of photos and videos from the scene.
"We are doing this methodically," he said, "... and with a sense of urgency."
Mayor: 'We will not let terror take us over'
At one point, 11 Boston-area hospitals had 23 people in critical condition and 40 listed as serious. There are still some fighting, with more surgeries planned. But there is progress. In fact, according to a CNN tally, at least 100 of the 183 people who received treatment were able to go home by Tuesday night.
How Boston and America recovers over the coming days, weeks and months remains to be seen.
As has happened before after such terror attacks, Tuesday saw authorities responding to alerts and threats -- in places like Dallas, Cleveland and New York -- that all proved to be unfounded.
Security in Los Angeles and New York has been stepped up in light of the Boston attack, and authorities in London are reviewing measures for that city's upcoming marathon.
Back in Massachusetts, one question is what becomes of the Boston Marathon -- the world's oldest annual marathon, dating to 1897, drawing more than 20,000 participants. Rather than shutting it down, officials promised to build the race back up.
"Next year's marathon will be even bigger and better," Gov. Deval Patrick.
That sense of defiance was echoed by Mayor Thomas Menino. Residents and visitors to the city might have to deal with more checks at transit stations and elsewhere. They might have to get used to seeing more authorities out and about. But they shouldn't change their attitudes, said the mayor.
"This tragedy is not going to stop Boston," Menino said. "We will not let terror take us over."