An Oklahoma-based missionary group working in Haiti’s capital was attacked by gangs Thursday night, leaving the daughter of a Missouri state representative, her husband and a third member of the group dead, a founder of the organization said.

David Lloyd III and his wife, Natalie, who were full-time missionaries, were attacked by gangs and killed Thursday evening, Lloyd’s mother said in an interview Friday.

Alicia Lloyd, who founded Missions in Haiti in 2000 with her husband, David Lloyd,…