A second excavation is planned in Tulsa, Okla., this week to unearth potential unmarked mass graves from a race massacre in 1921. In July, researchers began excavation at Oaklawn Cemetery, shown here. They found no evidence of human remains at that particular excavation site.

Work continues on an excavation of a potential unmarked mass grave from the 1921 Tulsa Race Massacre, at Oaklawn Cemetery in Tulsa, Okla., Tuesday, July 14, 2020. On May 31 and June 1 in 1921, white residents looted and burned Tulsa’s black Greenwood district, killing as many as 300 people with many believed buried in mass graves.  (AP Photo/Sue Ogrocki)