1. A declarant is “unavailable as a witness” if the declarant is:
(a) Exempted by ruling of the judge on the ground of privilege from testifying concerning the subject matter of the declarant’s statement;
(b) Persistent in refusing to testify despite an order of the judge to do so;
(c) Unable to be present or to testify at the hearing because of death or then existing physical or mental illness or infirmity; or
(d) Absent from the hearing and beyond the jurisdiction of the court to compel appearance and the proponent of the declarant’s statement has exercised reasonable diligence but has been unable to procure the declarant’s attendance or to take the declarant’s deposition.
2. A declarant is not “unavailable as a witness” if the declarant’s exemption, refusal, inability or absence is due to the procurement or wrongdoing of the proponent of the declarant’s statement for the purpose of preventing the witness from attending or testifying.