TULSA, Okla. (AP) — Archaeologists resumed searching a Tulsa cemetery on Tuesday but found no signs of human remains from victims of the 1921 Tulsa Race Massacre, state Archaeologist Kary Stackelbeck said.

The search of Tulsa’s Oaklawn Cemetery had thus far turned up only common household items such as broken bottles, in addition to a shell casing that is likely not related to the massacre, Stackelbeck said.

“I know that anything to do with firearms is going to be of interest,” but “shell casings ar going to something that is found at the scene of the crime, not the scene of the burial,” Stackelbeck said.

Researchers on Monday began opening an area where ground-penetrating radar earlier this year determined there was an anomaly consistent with mass graves.

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.

On May 31 and June 1, 1921, white residents and civil society leaders looted and burned Tulsa’s Black Greenwood District, known as Black Wall Street, to the ground and reportedly used planes to drop projectiles on it.

The attackers killed up to 300 Black Tulsa residents, many of whom were believed to have been buried in mass graves, and forced survivors for a time to live in internment camps overseen by National Guard members.