After hiking for more than 10 hours during a humanitarian medical mission—apparently unarmed and without security guards—Thomas Grams, a dentist from Durango, was among 10 helpers who were slaughtered in Afghanistan.

The Taliban, which has claimed responsibility for the executions, alleged that the members of the medical team were spies trying to convert Muslims to Christianity, reports The Associated Press.

Only the party’s Afghan driver survived the slayings, after he recited verses from the Koran while begging for his life. The members were traveling under the umbrella of the International Assistance Mission, a nongovernmental organization operating in Afghanistan, which is also registered as a Christian nonprofit group but does not proselytize.

Grams, a member of Denver-based Global Dental Relief, joined with IAM for the mission.

“This just breaks my heart,” Katy Shaw of Global Dental Relief tells 7News. “The claims that they were proselytizing or that they were spying couldn’t have possibly applied to Tom, they just couldn’t. I know that he’s been committed to doing this work for a very long time. He’s not in it for any sort of a mission other than helping individual people one by one.”

That sentiment is echoed in a report by Britain’s Guardian, in which the family of Karen Woo, a British doctor killed in the massacre, says she was a “true hero” who had no religious or political agenda.