"I have trouble going back to the finish line of the marathon, because I can visualize where everybody was when I photographed them," Tlumacki says.
He was especially haunted by the images he took of 17-year-old Sydney Corcoran and her 48-year-old mother, Celeste. Shrapnel severed Sydney's femoral artery and destroyed Celeste's lower legs.
"By photographing people the way I did -- Sydney on the ground, helpless, and Celeste -- I felt like I took advantage of them," Tlumacki says. "Even though I was doing my job, that I was guilty of maybe depriving them of their dignity."
Tlumacki felt compelled to meet them. Two weeks later, when he finally did, he apologized.
"I didn't want to have that image in my head of them laying on the ground," he says. "I needed a new picture of them, and I asked them if I could take a picture of them, and they just kind of looked at each other and smiled."
They grew closer as he documented their recovery.
"One of the first times that Celeste stood up by herself without holding on to anything ... that was, for me, day one of Celeste being energized and courageous, being Boston strong," Tlumacki says.
Tlumacki witnessed milestones, such as the day Sydney left the hospital.
"To just be in my brother's car and out of a hospital and to know I was going home, I was just so ecstatic, and I was like, 'Alright, take me home!'" Sydney recalls.
Five days later, Celeste came home.
"They wheeled me in, and I threw up my arms, just like she did," Celeste says. "And was just like, 'Yes, I'm home.'"
Another favorite was the night of Sydney's senior prom.
"There were times when we didn't think we'd be that happy again, or just be here physically," Sydney says. "To be able to look back and see that, there's a certain triumph in it, because you've overcome that obstacle."
Tlumacki says he now feels absolved of his guilt.
"I remember Celeste saying to me, 'John, I don't want you ever, ever to feel that guilt ever again. Whatever you did, people wouldn't have known the horror that day, what terrorism does, and you captured that for the world to see,'" Tlumacki says. "That's all I needed to hear. That was closure for me."After experiencing the bombing as strangers, they are healing together as friends.