He captured the image that told the story of the Boston Marathon bombing. Ten years later, he finally met the subject.

We both were so lucky we weren’t injured. I continued to shoot photos of those badly injured and being helped by first responders and spectators. I did not see Bill again until April 3 of this year, 10 years later. I flew across the country, to Marysville, Wash., to photograph him again — this time on our terms. I never really saw his face, just his body crumpled on the ground at my feet. It was Bill Iffrig, a 78-year old runner who fell hard when the first bomb exploded...