Although a prosecutor enjoys broad discretion in presenting evidence to a grand jury, the exercise of that discretion requires "conscientious judgment, not arbitrary action." . This exercise of discretion must be made in good faith, with the knowledge that her primary function as prosecutor "is not to convict, but to see that justice is done."

The grand jury as it is derived from common law and, in theory at least, as it still exists, is not simply an "accusatory" body. Its intended function is to act as a buffer against unfounded and arbitrary accusations, to stand independently between the accused and the state as a protector against arbitrary and unfounded governmental action.. Its duty is to sift accusations of criminal conduct, to protect individuals against arbitrary, oppressive and unwarranted criminal accusations, and to assess the likelihood of prosecutorial success.  Thus, it may be seen that the grand jury must act as a "shield" as well as a "sword".

In order to be able to fulfill its obligation to act independently of the government, the grand jury has a duty to inform itself as to both the facts and, the law relevant to a given case. See,. However, the courts have increasingly recognized a modern paradox to these requirements, in that "it is the prosecutor who draws up the indictment, calls and examines the grand jury witnesses, advises the grand jury as to the law and is in constant attendance during its proceeding.". Thus, it is clear that a grand jury "cannot be expected to call for evidence of which it is kept ignorant".

While a grand jury may receive and consider hearsay testimony during a course of its proceedings, our courts have likewise made clear that a grand jury action is fatally vitiated where the essence of the state's presentation is to call one investigator whose function is limited to "consigning the prosecutor's file to the grand jury and thereupon [leaving] the room."