(a) Definition of unavailability. "Unavailability as a witness" includes situations in which 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;(2) Persists in refusing to testify concerning the subject matter of the declarant's statement despite an order of the court to do so;(3) Testifies to a lack of memory of the subject matter of the declarant's statement;(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 the statement has been unable to procure the declarant's attendance by process or other reasonable means.A declarant is not unavailable as a witness if his 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.