What is the current state of the law on a grand jury subpoena?

Id. at 688 (citations omitted). Every person within the jurisdiction of the government has an obligation to appear and give his evidence before the grand jury. United States v. Dionisio, supra, 410 U.S. at 9-10.

"A grand jury's investigation is not fully carried out until every available clue has been run down and all witnesses examined in every proper way to find if a crime has been committed...." United States v. Stone, 429 F.2d 138, 140 (2 Cir.1970). It is part of the grand jury's function of protecting persons against arbitrary or unfair action to call before it persons suspected of criminal activity, and "persons suspected of no misconduct but who may be able to provide links in a chain of evidence relating to criminal conduct of others". United States v. Mandujano, supra, 425 U.S. at 573. "It is entirely appropriate--indeed imperative--to summon individuals who may be able to illuminate the shadowy precincts of corruption and crime." Id.

The majority's creation of a new requirement to be complied with by the government before it may enforce a grand jury subpoena can be justified only if the information sought is protected by a constitutional, common law, or statutory privilege. ⁷ See Branzburg v. Hayes, supra, 408 U.S. at 688.