Arizona v. Rumsey
In Arizona v. Rumsey, 467 U.S. 203, 209, 104 S.Ct. 2305, 2309, 81 L.Ed.2d 164 (1984), the Supreme Court determined that Arizona's capital sentencing proceeding "shares the characteristics of the Missouri proceeding described in Bullington v. Missouri, 451 U.S. 430, 101 S.Ct. 1852, 68 L.Ed.2d 270 (1981) that make it resemble a trial for purposes of the Double Jeopardy Clause."
The sentencer, the trial judge in Arizona, "is required to choose between two options: death, and life imprisonment without possibility of parole for 25 years." Id. at 209-10, 104 S.Ct. at 2309.
When the judge imposes a life sentence, after following detailed statutory standards related to aggravating and mitigating circumstances, "that judgment, based on findings sufficient to establish legal entitlement to the life sentence, amounts to an acquittal on the merits and, as such, bars any retrial of the appropriateness of the death penalty." Id. at 211, 104 S.Ct. at 2310.