What is the test for determining whether a witness was legally unavailable?

^2. Respondent asks us to utilize an abuse of discretion standard and find that no abuse of discretion occurred. We cannot analyze the case on that basis, as the issue of federal constitutional error was raised below and has been repeated on appeal. We utilize independent review in analyzing the issue. (People v. Cromer (2001) 24 Cal.4th 889, 901-902 [independent review, not abuse of discretion, standard applicable to whether witness was legally unavailable].)