It's the group of people in Georgia that are investigating the possibility that certain people attempted to tamper with the results of the 2020 election in the state. That's not the normal function of a grand jury though:
Special grand jury:
While a regular grand jury primarily decides whether to bring charges, a special grand jury is called into existence to investigate whether organized crime is occurring in the community in which it sits. This could include, for instance, organized drug activity or organized corruption in government.
For background regarding the this current special grand jury:
- Fulton grand jury subpoenas Giuliani, Graham, Trump campaign lawyers.
- Fulton grand jury probe of 2020 election conduct zeroes in on Trump’s inner circle.
- District attorney in Georgia asks for a special grand jury for Trump election probe.
Grand juries are mentioned in the 5th Amendment.
Here's more on this particular one:
- Fulton County.
- Fulton County Grand Jury.
- Fulton County District Attorney Fani Willis.
