Depends on the trial, where it's happening, and the prosecutors' feelings towards it. The mil version of a grand jury is a mini hearing in front of a single investigating officer (IO) (who until recently was a 'randomly' picked non lawyer) with defense present and able to call witnesses and present evidence but the decisions made to charge or not by the IO aren't binding and can be overruled, almost always by someone who barely skims the highlights and follows the JAGs advice. Most Fed GJ are secret and locked down until/unless someone is charged. The majority of state GJ fall somewhere in the middle. Some prosecutors, especially with cases that they don't really want to try, either weak or politicized (like a seemingly weak self-defense shooting claim in a conservative area) will have full defense participation so they can blame the GJ for not indicting.
TL/DR: A grand jury is almost always a formality so the state can say that one person didn't make a decision to charge someone.