Grand Juries hear evidence and testimony then vote on the question ‘is there a criminal case to answer?’.
If the Grand Jury votes yes, it then remains for prosecutors to decide if they wish to proceed with a prosecution.
The decision might be No, because the case isn’t strong enough/yet strong enough. No, because we want to work a cooperation deal with the accused. No because we’ll come back to it later.
Or of course, Yes.
My punt is for later charges against Flynn, while Graham might cut a deal.
Eitherway, this looks as though it has legs.
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I think the OP is mistaken, it was the special Grand Jury that handed down the indictment decisions, the Prosecutors haven’t (yet) put the evidence against Graham and Flynn before the actual Grand Jury.