TULSA — The mayor was about to take a bite of his pecan waffle at his favorite breakfast spot when a white woman stalked up to his table, pointed her finger and lit into him about his decision to reopen an investigation into a century-old race massacre.

“You are doing this to make white people feel bad,” the woman told G.T. Bynum as he and his wife and two children were eating at Phill’s Diner on a recent Sunday morning.

The waitress tried to get the woman to sit down, Bynum said, but she refused, angered by the city’s plan to dig for bodies from the 1921 massacre, one of the worst episodes of racial violence in U.S. history. The excavation at Oaklawn Cemetery, where ground-penetrating radar revealed a “large anomaly” that could be a mass grave, is scheduled to begin April 1.

Bynum, a white Republican in deeply red Oklahoma, tried to explain the unresolved questions about a rampage historians believe left as many as 300 black people dead. As other customers looked on, he said he would not back down from trying to find answers to what happened.