Charlie Johnston ran the marathon last year and he was at the finish line just a few minutes before it happened. During the explosions he was on a train under the Boston Harbor, and he said he couldn't believe what he was seeing when they resurfaced.
"It went from a really great day on that train to when we got off everything started crumbling and we started realizing what had happened," Johnston said.
Despite the chaos Johnston saw after the Boston Marathon bombing, he said he never thought about not running it again.
"26.2 miles is the same no matter where you run it, but Boston just the energy is palpable," he said.
This will be the sixth time he's run it.
"If that race could ever have more of a celebratory atmosphere than it already does, this is going to be the year that it happens," Johnston said.
"They're anticipating more than one million people to line that course," said Brian Sooudi.
This will Sooudi's first Boston Marathon.
"This is not just a 26-mile run anymore," Sooudi said. "It's going to be a remembrance of the victims, the survivors, the city of Boston."
Sooudi said he's not nervous for the run itself, but for the high emotions that will come with it.
"There will be tears shed and laughter and everything else in between," he said.
For runners the Boston Marathon has always been the ultimate race to run, and Johnston said it always will be.
"There are places in this world where you take a piece of it with you and you leave a piece of you there, and Boston is always going to have a special place in my heart," Johnston said.
Johnston and Sooudi will join about 36 thousand runners running in this year's Boston Marathon on Monday.