In what circumstances will a court allow a jury to infer that all heroin seized in a possession case was imported?

3. Where there is evidence of possession, the court can instruct that the law permits the jury to infer both importation and the defendant's knowledge. The court, however, must make it clear that the jury is not required to draw either inference, and that the permissible inferences do not shift the burden of proof nor require the possessing defendant to testify or come forward with evidence. Cf. United States v. Crespo, supra, 422 F.2d at 720 n. 2.

4. The court may not instruct the jury that all heroin is imported. Any discussion of the likelihood that the heroin involved was imported should make it clear that the court is only stating reasons why the inference is a reasonable one, but that the jury is still free not to draw the inference. Cf. Turner v. United States, supra, 396 U.S. at 406, 90 S.Ct. 642.