precisely Thomas’ Fifth Amendment privilege that brought the Confrontation Clause into this case in the first place: although the State “produced” Thomas in court, his right not to testify against himself made him effectively unavailable for cross-examination by petitioner. See Douglas v. Alabama, 380 U. S. 415, 419 (1965). In much the same way, Thomas’ testimony was unavailable to the State. See Phillips v. Wyrick, 558 F. 2d 489, 494 (CA8 1977), cert. denied, 434 U. S. 1088 (1978).
Illinois, of course, had weapons that petitioner lacked. For example, the State could have offered Thomas a favorable sentencing recommendation, or the opportunity to plead guilty to a lesser offense', in exchange for his testimony against petitioner. Alternatively, the State could have tried Thomas separately and granted him immunity from the use of his inculpatory testimony against petitioner. See Kastigar v. United States, 406 U. S. 441 (1972). Measures of this kind, however, entail significant costs. A plea agreement necessarily compromises the community’s legitimate correctional interests, and a grant of immunity places a heavy evidentiary burden on any future prosecution of the witness. See id., at 460-461. I cannot conclude that the possibility of such an arrangement with petitioner’s codefendant rendered him an available witness for purposes of the Confrontation Clause.
My unwillingness reflects in part a respect for established principles of the law of evidence. Although the Confrontation Clause differs in significant ways from the common-law rule against the introduction of hearsay, the two “stem from the same roots,” Dutton v. Evans, 400 U. S., at 86 (plurality opinion), and “protect similar values,” California v. Green, 399 U. S., at 155. As a consequence, analysis under the Confrontation Clause properly is informed, although not constrained, by hearsay principles developed over time by courts and legislatures. See, e. g., Roberts, 448 U. S., at 66. Among those principles is the generally accepted notion that