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.' " Branrburg v. Hayes. 408 U.S. 665, 701, 92 S.Ct. 2646, 2667, 33 L.Ed.2d 626 (1972) (quoting United States v. Stone, 429 F.2d 138, 140 (2d Cir.1970)); In re G