Conspiracy is a continuing offense. For statutes such as 18 U.S.C. § 371, which require an overt act in furtherance of the conspiracy, the statute of limitations begins to run on the date of the last overt act. See Fiswick v. United States, 329 U.S. 211 (1946); United States v. Butler, 792 F.2d 1528 (11th Cir. 1986). For conspiracy statutes which do not require proof of an overt act, such as RICO (18 U.S.C. § 1961) or 21 U.S.C. § 846, the government must allege and prove that the conspiracy continued into the limitations period. The crucial question in this regard is the scope of the conspiratorial agreement, and the conspiracy is deemed to continue until its purpose has been achieved or abandoned. See United States v. Northern Imp. Co., 814 F.2d 540 (8th Cir. 1987); United States v. Coia, 719 F.2d 1120 (11th Cir. 1983), cert. denied, 466 U.S. 973 (1984).
An individual's "withdrawal" from a conspiracy starts the statute of limitations running as to that individual. "Withdrawal" from a conspiracy for this purpose means that the conspirator must take affirmative action by making a clean breast to the authorities or communicating his or her disassociation to the other conspirators. See United States v. Gonzalez, 797 F.2d 915 (10th Cir. 1986).