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.

United States v. Reed, 227 F.3d 763, 737 (7th Cir. 2000) (upholding trial court's ruling to admit Simmons's prior testimony because he was unavailable, as Federal Rule of Evidence 804(a)(1) considers a declarant as....The hearsay exceptions created by Federal Rule of Evidence 804 or a comparable State rule apply only if the declarant (the maker of the statement) is unavailable to testify at the trial or proceedings at which the declarant's statement is offered.

United States v. Maliszewski, 161 F.3d 992, 1009 (6th Cir. 1998) (upholding trial court's admission of the Mireles testimony [about defendant's repeated statements made by her dead husband] because at the time of the trial,....For purposes of the hearsay exceptions created by Federal Rule of Evidence 804 or a comparable State rule a declarant is "unavailable" within the meaning of Rule 804(b) or a comparable State rule if the declarant is unable to be present or to testify at the hearing because of death or then existing physical or mental illness or infirmity; but a declarant is not "unavailable" if the declarant's absence is due to the procurement or wrongdoing of the proponent of a statement for the purpose of preventing the witness from attending or testifying.

United States v. Magallanez, 408 F.3d 672, 680 (10th Cir. 2005) (upholding the trial court's admission of testimony of a government rebuttal witness; held, witness' testimony was not character evidence, but was properly introduced as rebuttal evidence which is not violative of either Rule 608 or Rule 404).If a criminal defendant offers evidence of his or her character circumstantially - to show he or she did not commit the crime charged -- the prosecution can offer rebutting evidence of defendant's character.