Boston Marathon runners tell their story of survival

(CBS News) BOSTON - For the spectators at the marathon -- whether they lived or died , were injured or unharmed -- was at least in part a matter of luck and where they were standing. Here is one survivors' story.

Long-distance running is a shared passion for David Comstock and Susie Eisenberg-Argo. The couple is from Texas.

"When you cross that finish line," said Comstock, "you're not just crossing 26.2 miles. You're crossing probably 3,000 miles of training leading up to that event."

This was his sixth Boston Marathon and her tenth.

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"We agreed that she would run on the right side so that when she finished in the crowds," said Comstock, "I could pick her out and she could pick me out."

"And about a hundred yards to finish," Eisenberg-Argo said, "the bomb goes off."

From a photograph, you can see her at the moment of the second explosion.

"I look," said Eisenberg-Argo. "I see the smoke coming out of the buildings. My immediate reaction was just shock." As for what the bomb felt like, she added: "It was an explosion. I felt just debris hit me but I didn't know what...it was so quick, I didn't know what had happened."

"I was extremely worried," said Comstock. "I didn't know where she was. I knew that she was expected to finish at the time right when the blast occurred."

"I'll kept going until I heard Dave screaming my name," said Eisenberg-Argo.

When she came through, according to Comstock, it was a moment of elation.

"The moment that we saw each other, we just embraced," said Eisenberg-Argo.

Had she thought about what might have happened if she'd been on the other side of the road? "Why we chose to go on the right side - it was meant to be," she said.

They say they'll run in next year's Boston Marathon to prove to whoever did this that life isn't defined by a single moment, but by many.