First-time marathoner Andrea Kalsow was on mile 21 of the Boston Marathon course when she heard bombs had wreaked havoc at the finish line.
"In that instant I knew my run was over," Kalsow, 23, of Brighton, Mass., told ABCNews.com
One in four of the elite runners who'd spent months training for the Boston Marathon couldn't cross the finish line and collect their medals before the blasts ended the race.
COMPLETE COVERAGE: Boston Marathon Explosion
PHOTOS: Boston Marathon Bombings Bring Out...Full Story