What is the effect of ambiguous jury instructions in a prosecution for mail and wire fraud?

Appellants rely on United States v. Mastelotto, 717 F.2d 1238 (9th Cir.1983), which held that in a prosecution for mail and wire fraud, defendant's right to a unanimous jury verdict is infringed when the court fails to instruct the jurors that they must all agree on the existence of, and defendant's participation in, the same scheme to defraud. In Mastelotto, the defendants claimed that a variance occurred between the single scheme charged in each count of the indictment and the proof at trial. Id. at 1247. The panel in Mastelotto reversed the conviction because it found that the jury instructions failed to require each juror to agree on the same single scheme to defraud as that charged in the indictment. Id. at 1250-51.

Similarly, in United States v. Echeverry, 698 F.2d 375 (9th Cir.1983), modified, 719 F.2d 974 (9th Cir.1983), this court reversed the defendant's conviction because an ambiguous jury instruction permitted the jury to convict without unanimously agreeing whether the proof showed the existence and duration of a single conspiracy or of

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