Federal Rules of Evidence (2003) Article VIII. Heresay, page 4

(5) [Other exceptions.][Transferred to Rule 807 ]

(6) Forfeiture by wrongdoing. A statement offered against a party that has engaged or acquiesced in wrongdoing that was intended to, and did, procure the unavailability of the declarant as a witness.

Rule 805. Hearsay Within Hearsay 
Hearsay included within hearsay is not excluded under the hearsay rule if each part of the combined statements conforms with an exception to the hearsay rule provided in these rules.

Rule 806. Attacking and Supporting Credibility of Declarant 
When a hearsay statement, or a statement defined in Rule 801(d)(2)(C), (D), or (E) , has been admitted in evidence, the credibility of the declarant may be attacked, and if attacked may be supported, by any evidence which would be admissible for those purposes if declarant had testified as a witness. Evidence of a statement or conduct by the declarant at any time, inconsistent with the declarant's hearsay statement, is not subject to any requirement that the declarant may have been afforded an opportunity to deny or explain. If the party against whom a hearsay statement has been admitted calls the declarant as a witness, the party is entitled to examine the declarant on the statement as if under cross-examination.

Rule 807. Residual Exception 
A statement not specifically covered by Rule 803 or 804 but having equivalent circumstantial guarantees of trustworthiness, is not excluded by the hearsay rule, if the court determines that (A) the statement is offered as evidence of a material fact; (B) the statement is more probative on the point for which it is offered than any other evidence which the proponent can procure through reasonable efforts; and (C) the general purposes of these rules and the interests of justice will best be served by admission of the statement into evidence. However, a statement may not be admitted under this exception unless the proponent of it makes known to the adverse party sufficiently in advance of the trial or hearing to provide the adverse party with a fair opportunity to prepare to meet it, the proponent's intention to offer the statement and the particulars of it, including the name and address of the declarant.