Is a prosecutor permitted to express his belief in the credibility of a government witness?

Although a prosecutor generally may not express his belief in the credibility of a government witness, United States v. McKoy, 771 F.2d 1207, 1210-11 (9th Cir.1985), he must be given a reasonable latitude to fashion a closing argument. United States v. Molina, 934 F.2d 1440, 1445 (9th Cir.1991). "Inherent in this latitude is the freedom to argue reasonable inferences based on the evidence," including the inference that, in a case with two conflicting stories, "one of the two sides is lying." Id. In United States v. Laurins, 857 F.2d 529 (9th Cir.1988), cert. denied, 492 U.S. 906 (1989), we held that a prosecutor's statement that the defendant was a liar was not plain error where the prosecutor "indicated that it is 'after listening to all the evidence' that he reached that conclusion." Id. at 539. Based on this qualifying language, this court concluded that the jury could have construed the prosecutor's statement as a comment on the evidence rather than as an assertion of personal belief. Id.