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.
PHOTOS: Boston Marathon Bombings Bring Out the Rescuer in Bystanders
For those 5,000-plus people it was a frustrating end to a day that was supposed to end in celebration.
"It's heartbreaking because you train so hard," runner Paula Smart told ABCNews.com.
Smart, who was running the marathon to celebrate turning 40 on Friday and giving birth to twins one year ago, said she was sidelined at mile 25.
"I'm angry and I'm disappointed," she said. "But you have to be thankful you have your life and your family."
Despite the bomb blasts that marred this year's event, organizers of the Boston Marathon said they would still hold the 118th edition of the famed race next year.
Marathoners who didn't finish the race have until Friday to pick up bags they had checked, according to the Boston Marathon's Facebook page. Many runners who couldn't finish posted that they were given their medals when they picked up their bags.
Andrew Quan, 33, of New York City was on track to break a personal record in his third marathon when he was stopped at mile 26, two-tenths of a mile from the finish line.
Quan had picked up his bag on Monday but said he'd returned home before he heard that medals were being handed out to the sidelined runners.
"At this point, I feel like I didn't quite finish it. I don't know If I want it," he said. "But at the same time, it's slightly symbolic."
Quan said he may sign up for another race soon to "get over this feeling of incompleteness."
He also has three marathons lined up for the fall in Berlin, Chicago and New York.
Kalsow, who would have finished her first marathon on Monday, plans to cross the finish line at the Providence, R.I., Marathon on May 12.
"It will be a victory for me, my city, and for all of the Boston Marathon runners who did not finish the race," she said.