reality that the United States is the only country in the world that continues to give official sanction to the juvenile death penalty. This reality does not become controlling, for the task of interpreting the Eighth Amendment remains our responsibility. Yet at least from the time of the Court’s decision in Trop [v. Dulles], the Court has referred to the laws of other countries and to international authorities as instructive for its interpretation of the Eighth Amendment’s prohibition of “cruel and unusual punishments.” 356 U.S. [86], at 102-103, 78 S.Ct. 590 [2 L.Ed.2d 630 (1958) ] (plurality opinion) (“The civilized nations of the world are in virtual unanimity that statelessness is not to be imposed as punishment for crime”); see also Atkins, supra, at 317, n. 21, 122 S.Ct. 2242 (<HOLDING>); Thompson [v. Oklahoma, 487 U.S. 815], supra,
holding that the death penalty was categorically prohibited for juvenile offenders holding that mentally retarded capital murderers are constitutionally ineligible for death penalty recognizing that within the world community the imposition of the death penalty for crimes committed by mentally retarded offenders is overwhelmingly disapproved holding the death penalty unconstitutional for mentally retarded defendants holding the eighth and fourteenth amendments forbid imposition of the death penalty on offenders who were under the age of eighteen when their crimes were committed