What is the burden of proving an unavailable witness?

reasonableness. (People v. Herrera, supra, 49 Cal.4th at p. 622.) Additionally, the Evidence Code defines an unavailable witness as one who is "[a]bsent from the hearing and the proponent of his or her statement has exercised reasonable diligence but has been unable to procure his or her attendance by the court's process." (Evid. Code, 240, subd. (a)(5).) The prosecution bears the burden of demonstrating the unavailability of its witness. (People v. Herrera, at pp. 622-623.)