Christopher Simmons (defendant) was sentenced to death following his conviction for a murder occurring when he was seventeen years old. Simmons challenged his conviction on the ground that the application of the death penalty to a minor is unconstitutional and is not supported by international law. The United States Supreme Court previously considered constitutional challenges to the juvenile death penalty in Thompson v. Oklahoma, 487 U.S. 815 (1988), where a plurality held that the Eighth and Fourteenth Amendments to the United States Constitution, as well as trends in international law, prohibited application of the death penalty to persons under age sixteen at the time of commission of the crime. The dissent strongly opposed the consideration of international practice on any matters relating to interpreting the United States Constitution. However, in Stanford v. Kentucky, 492 U.S. 361 (1989), on the issue of the constitutionality of the death penalty applied to persons aged sixteen and seventeen, the application of the death penalty was upheld. Simmons argued in Missouri state court that after the Stanford decision, a new national consensus developed opposing application of the death penalty to juveniles which was supported by international law and foreign practice. The Missouri Supreme Court agreed, and Roper (plaintiff) appealed to the United States Supreme Court.