Does vouching in a criminal case affect the credibility of the evidence at trial?

Here, even if vouching occurred, we conclude that the challenged statements do not rise to the level of harmless error because the trial judge gave an appropriate curative instruction in each instance. See United States v. Endicott, 803 F.2d 506, 513 (9th Cir.1986) (trial judge's instruction can neutralize the effect of inappropriate prosecutorial comments). The district court cured the effect of the first instance of vouching when it instructed the jury that the ranch owner's statements should be examined with greater caution than those of an ordinary witness because the ranch owner was an accomplice to the crime. Cf. United States v. Shaw, 829 F.2d 714, 718 (9th Cir.1987) (prosecutorial vouching held to be harmless error where trial court instructed the jury that the testimony of a witness who was the beneficiary of a plea bargain should be examined with greater caution than the testimony of an ordinary witness), cert. denied, 108 S.Ct. 1157 (1988). Similarly, the district court cured the effect of the vouching on closing argument when it told the jury that the lawyer's statements during closing argument were not evidence. See Endicott, 803 F.2d at 513.