“ In my view, the question whether petitioner had a right to judicially immunized testimony at the penalty phase of the proceedings cannot be avoided on these terms. The California Supreme Court was mistaken in presuming that it could resolve the disposition of petitioner's claim to judicially immunized testimony at the penalty phase of a capital proceeding by the same standard used to assess a defendant's right to immunized testimony at trial. It is well established that a criminal defendant's entitlement to present useful evidence is at its strongest in the capital sentencing context ”

“ Lynaugh, 492 U.S. 302, 318, 109 S.Ct. 2934, 2946, 106 L.Ed.2d 256 (1989) (emphasis added) ; accord, Skipper v. South Carolina, 476 U.S. 1, 4, 106 S.Ct. 1669, 1671, 90 L.Ed.2d 1 (1986) ; Eddings v. Oklahoma, 455 U.S. 104, 114-115, 102 S.Ct. 869, 876-877, 71 L.Ed.2d 1 (1982) . ”