The U.S. state of Georgia was hotly contested in the last presidential election, and it’s still under scrutiny ahead of this year’s congressional midterms.

The district attorney in the state’s largest county is looking into whether former President Trump acted illegally in efforts to overturn the 2020 results, which President Biden won.

A special grand jury will start hearing testimony in May. A key witness is likely to be Georgia’s secretary of state, who Trump tried to pressure to help overturn the results.