What is the burden of proving that a preindictment delay caused prejudice?

"To establish a Fifth Amendment violation, [Defendant] must show that [s]he suffered actual, non-speculative prejudice from the delay and that the delay, when weighed against the government's reasons for it, offends those fundamental conceptions of justice which lie at the base of our civil and political institutions." Id. at 1165. The "burden of proving that a preindictment delay caused actual prejudice is a heavy one." Id.; see also United States v. Huntley, 976 F.2d 1287, 1290 (9th Cir. 1992) (noting that "[t]he task of establishing the requisite prejudice for a possible due process violation is 'so heavy' that we have found only two cases since 1975 in which any circuit has upheld a due process claim.").