Shortly after Harpreet Singh of Grafton learned about the shooting at a Sikh temple in Oak Creek, Wis., where a gunman killed six people before police fatally shot him, anxious inquiries started pouring in from Sikhs in the Milwaukee area.

Singh, a veterinarian resident at Tufts University, said he has long been a central figure at the temple. As one of its most fluent English speakers, he often spoke for his largely misunderstood religious minority, and he gave community classes on Sikh culture.