Representative John Williamson of the Mennonite Central Committee describes 40-year-old Lancaster resident Glen Lapp as a "very kind, loving, respectful person."
Williamson says Lapp was due to finish a two-year assignment in Afghanistan in October.
The Taliban has claimed responsibility for the Thursday shooting deaths of Lapp and nine other volunteers, saying the workers were trying to convert Muslims to Christianity.
But Williamson says any claims that Lapp's group was proselytizing in the region are "rubbish."
Lapp was working with a charity that was providing eye care and other medical services in the war-torn country.