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(a) or a comparable State rule if the declarant (1) is exempted by ruling of the court on the ground of privilege from testifying concerning the subject matter of the declarant's statement; or (2) persists in refusing to testify concerning the subject matter of the declarant's statement despite an order of the court to do so; or (3) testifies to a lack of memory of the subject matter of the declarant's statement; or (4) is unable to be present or to testify at the hearing because of death or then existing physical or mental illness or infirmity; or (5) is absent from the hearing and the proponent of a statement has been unable to procure the declarant's attendance (or in the case of a hearsay exception under subdivision (b)(2), (3), or (4) of Rule 804(b) or a comparable State rule, the declarant's attendance or testimony) by process or other reasonable means; but a declarant is not "unavailable" if such exemption, refusal, claim of lack of memory, inability, or 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.