ATLANTA — As a 20-year-old civil rights activist in 1968, Tyrone Brooks drove 40 miles from Atlanta to Walton County to meet Dan Young, who ran the county’s only black funeral home. “Young man, I want to show you something,” Brooks remembers Young telling him. In the funeral home’s basement, Young pulled out a folder containing photographs of bodies — the victims, Young told Brooks, of the last open public mass lynching in the United States. “That really got my attention,” said Brooks, now a representative in the Georgia House. Nearly 40 years later, those disturbing photos still have Brooks’...