What is the burden of proving action in furtherance of a conspiracy?

1 This rule creates a presumption that one who acts in furtherance of a conspiracy knows of the conspiracy's existence. We need not decide whether proof of action in furtherance of a conspiracy also raises a presumption of intent to commit the underlying offense, (see, e.g., United States v. Perez, 491 F.2d 167 (9th Cir.), cert. denied, 419 U.S. 858, 95 S.Ct. 106, 42 L.Ed.2d 92 (1974) (no direct evidence of intent to possess and distribute heroin)), because the government failed to carry its burden of proving an act in furtherance of conspiracy in this case.