Dressed in Boston’s yellow-and-blue official marathon gear with a medal around his neck, Michael Kaplinidis stood near the metal barriers blocking off Boylston Street on Tuesday, his eyes fixed on the finish line a block away.

“I’ve had tears in my eyes all morning,” said Kaplinidis, who grew up in Dorchester and ran in Monday’s race to raise money for a local school charity. He looked down at a makeshift memorial that had been arranged on the guardrail—flowers, balloons, cards, Boston Red Sox T-shirts, and Bengay, a topical pain reliever for sore muscles.

But nothing could numb the aches and pains of a city grieving in the aftermath of Marathon Monday’s attacks, which killed three people and injured at least 140 others. Bostonians, marathon runners, and others mourning Monday’s losses crowded the Back Bay area, taking pictures of abandoned aluminum blankets and other detritus on the barricaded streets.

“When you look down that road you feel like you left something behind,” said Morten Fogh, who came from Toronto with four friends to run in the race. “Some people will never walk again, never see again or hear again. We’re going to have to try and separate the tragedy from an incredible marathon experience, because we want to remember some of the positives as well.”

If a silver lining had emerged by Tuesday, it was a sense of unity, from the law enforcement officials working with federal agents to the heroes who ran toward danger and the volunteers who supported runners at every mile.

“If it weren’t for the support groups, my dad and I might not have been able to find my mom,” said one 9-year-old boy, sticking close to his mother, Caron Trakman, as they both spoke to reporters.

After finishing the race with a group of four from San Diego, Trakman returned to her hotel room Monday with her husband and son when they heard a blast followed by sirens.

“The outcome could have been very different for my family,” Trakman told The Daily Beast, quietly saying a prayer for Martin Richard, the 8-year-old boy from Dorchester who was killed in the bombings.

She recognized how the incident had affected her son, who peppered her with questions over dinner Monday night. “He asked me, ‘Mom, what’s terrorism? Why do people do that?’’”

Less than six months after the Sandy Hook Elementary School massacre, parents and educators must once again discuss a national tragedy with their children.

“It was difficult,” said Trakman. “We’re all here as adults, but he’s right in the middle of it with us, and he’s at such an impressionable age.”

Other parents held their kids’ hands a little tighter in Boston on Tuesday.

“These guys were about 50 yards from the second bomb explosion just a few hours before it happened,” said Wayne Crews of his wife, 6-year-old son, and 7-year-old daughter, who had all come from their home in South Carolina to watch him run his fifth marathon.

“Our daughter saw the news and she’s been a bit scared that other bombs might go off,” said Crews’s wife, adding that they were heading to the New England Aquarium for a welcome distraction.

Outside Back Bay, at least 17 patients remained in critical condition in various hospitals throughout the city. Later in the afternoon, the FBI stated that the explosives were found in black nylon bags that were converted pressure-cookers packed with shrapnel. Krystle Campbell, a 29-year-old woman from Medford, Mass., was identified among the three dead.

On Tuesday evening, hundreds gathered in Boston Common for a vigil for the victims—one one of several around the city—where they held hands and banners that read “Peace here and everywhere” and “Boston you’re our home.”

Sarah Remes, 25, noted how everyone wore their blue-and-yellow gear into the evening. “Whether they ran or volunteered, everyone was still wearing their marathon clothes all day,” she said. “It was pretty cool to see.”