A witness may be impeached by evidence that the witness was not in a position to observe or perceive the matter about which the witness testifies.

Cf. United States v. Iribe-Perez, 129 F.3d 1167, 1173 (10th Cir. 1997) (reversing conviction for conspiracy to distribute cocaine even though the defendant's compulsory process right was not violated when the government allowed....The prohibition, grounded in the Compulsory Process Clause, against deliberate government action that deprives a criminal defendant of the relevant and material exculpatory testimony of a witness may effectively limit the government's use of hearsay evidence against a criminal defendant.

United States v. Johnson, 440 F.3d 832, 846-847 (6th Cir. 2006) (upholding trial court's admission of Stone's statements [which were recorded surreptitiously by Hardin at the behest of the government] as statements against....Federal Rule of Evidence of Evidence 804(b)(3) or a comparable State rule creates a hearsay exception for a statement which was at the time of its making so far contrary to the declarant's pecuniary or proprietary interest, or so far tended to subject the declarant to civil or criminal liability, or to render invalid a claim by the declarant against another, that a reasonable person in the declarant's position would not have made the statement unless believing it to be true. A statement tending to expose the declarant to criminal liability and offered to exculpate the accused is not admissible unless corroborating circumstances clearly indicate the trustworthiness of the statement.

Karme v. Commissioner, 673 F.2d 1062, 1065 (9th Cir. 1982) (holding, in taxpayers' claim for deduction, that the tax court properly admitted into evidence the bank records and testimony under the residual hearsay....The hearsay exception created by Federal Rule of Evidence 807 or a comparable State rule applies only if the the affected statement is more probative on the point for which it is offered than any other evidence which the proponent can procure through reasonable efforts.