A runner retrieves his belongings from a Boston Athletics Association worker at a sorting area near the site of an explosion. Associated Press

The Boston Athletic Association on Wednesday opened its headquarters near Copley Square to Boston Marathon runners looking to retrieve bags and claim their medals.

A spokesperson for the BAA, which organizes the race, said early Wednesday that the office would remain open until 8 p.m. that night and from 11 a.m. through 8 p.m. Thursday and Friday. The spokesperson declined to comment about the BAA's role in the ongoing investigation of the Monday bombing that killed three spectators and injured more than a 170 others near the finish line of the Boston Marathon.

Runners began streaming into the BAA offices mid-morning Wednesday, some wearing their race bibs. After a typical race, the number on those bibs is used to identify which checked bags belong to whom. But following the bombings, there was little or no opportunity Monday for runners to reclaim their checked belongings or finish the race to claim a medal.

On Wednesday, the mood was subdued, with runners expressing mixed feelings about claiming medals for a race many didn't finish.

"I definitely feel like I have unfinished business," said Kathleen Lutz, 44, from Auburn, Mass. She was twenty-five miles into her sixth Boston Marathon as a charity runner with the Dana Farber organization when "a cop just grabbed me by the shoulder and said, 'The race is closed, you have to stop.'"

She said she hesitated to retrieve her medal because she didn't feel as though she had earned it. Lutz said she wants to run Boston again, but adamantly does not want her husband or three children to attend, as they did this year.

"I put them in harm's way," she said, her eyes welling with tears. "They were there because of me. Even if they catch who did this, it won't be enough. I don't want my family to come."

"They attacked the best of humanity. It's families, it's children. One of those who died was an 8-year-old boy. I have an 8-year-old boy," Lutz said, her voice trailing off.

Write to Sara Germano at sara.germano@wsj.com