In Missouri, a judge picks the members of the GJ, I think most states are the same in this regard. That judge, whoever he/she is, extended the jurors time to serve in the DW v. MB incident. The GJ is really in charge of the whole process and the prosecutor sort of facilitates the process. A GJ is a travesty of justice because the prosecutor is the only one who presents the evidence to charge, take the citizen to a criminal trial. If the GJ don't know the exculpatory evidence exists they never know to ask for it.
A defense lawyer could have exculpatory evidence that indicates that the accused did not meet the requirements of the law he is charged with and as such should not be charged with the crime. The railroaded citizen only gets his chance to present his exculpatory evidence after he has been indicted and is then subject to a criminal trial.
Where does it say in the Constitution that the GJ proceedings must be secret? Where does it say in the Constitution that both sides do not get to preset their evidence to the GJ? Why are witnesses valued when called by a GJ, but those same witnesses are not valued during a criminal trial.