In a line of cases reaching back to Weems v. United States (1910) the Supreme Court has elaborated that the Eighth Amendment protects the dignity of all persons, "even those convicted of heinous crimes".

The Supreme Court has restricted death sentences by crime (see Coker v. Georgia and Enmund v. Florida) and class of offender (see Thompson v. Oklahoma, Ford v. Wainwright and Atkins v. Virginia).

The court found there was no national consensus that the execution of older adolescents was cruel and unusual under "evolving standards of decency" because the sentence was still permitted by a majority of death penalty jurisdictions.

[3] Justice Sandra Day O'Connor, concurring in the Stanford judgment, was critical of the plurality's refusal "to judge whether the nexus between the punishment imposed and the defendant's blameworthiness is proportional."

In the Roper decision, Justice Kennedy, writing for the majority, said the Stanford plurality had failed “to bring its independent judgment to bear on the proportionality of the death penalty for a particular class of...offenders".

[4] In the state of Missouri in 1993, 17-year-old Christopher Simmons concocted a plan to commit burglary and murder, having previously told friends that he "wanted to kill someone" and that he "believed he could get away with it because he was a minor".

[21] However, in light of a 2002 U.S. Supreme Court ruling, in Atkins v. Virginia,[22] that overturned the death penalty for the intellectually disabled, Simmons filed a new petition for state post-conviction relief.

[25] Under the "evolving standards of decency" test, the Court held that it was cruel and unusual punishment to execute a person who was under the age of 18 when the crime was committed.

The majority reasons that adolescents are not likely to be deterred, quoting from the Thompson plurality opinion to explain that imposing the death penalty would not serve a deterrent purpose for a class of prisoners who were unlikely to engage in "the kind of cost benefit analysis that attaches any weight to the possibility of execution".

[29] The majority rejects the view taken by the dissent that youth was a mitigating factor to be taken into consideration during sentencing:[27] If trained psychiatrists with the advantage of clinical testing and observation refrain, despite diagnostic expertise, from assessing any juvenile under 18 as having antisocial personality disorder, we conclude that States should refrain from asking jurors to issue a far graver condemnation that a juvenile offender merits the death penalty.Finally, Justice Kennedy supports the Court's decision by looking to trends in other countries.

[26] In addition, Justice Scalia also objected in general to the Court's willingness to take guidance from foreign law in interpreting the Constitution:[26] Though the views of our own citizens are essentially irrelevant to the Court's decision today, the views of other countries and the so-called international community take center stageHe accused the majority of invoking foreign law selectively.

His dissent cited a passage from The Federalist Papers in arguing that the role of the judiciary in the constitutional scheme is to interpret the law as formulated in democratically selected legislatures.

Furthermore, she was skeptical of the Court's conclusion about diminished culpability for those who committed crimes before they turned 18 because the "mitigating characteristics associated with youth [did] not justify an absolute age limit".

[26] Because the Roper majority's finding of a national consensus was weak (twenty states still allowed executions for crimes committed by older adolescents), the Court was persuaded that foreign jurisdictions could provide "respected and significant confirmation" for their proportionality analysis.

Writing for the majority in Stanford Justice Scalia did not take the sentencing practices of foreign countries into consideration: "it is American conceptions of decency that are dispositive.

[27] The impact of this ruling was immediately felt in the State of Virginia, where Lee Boyd Malvo became no longer eligible for the death penalty for his role in the Beltway sniper attacks in October 2002.

[citation needed] At the outset of the Beltway sniper prosecutions, the primary reason for extraditing the two suspects from Maryland, where they were arrested, to Virginia, was the difference in how the two states deal with the death penalty.

[citation needed] After the Roper decision the APA filed briefs in Graham v Florida and Miller v. Alabama arguing that life without parole sentences for minors were unconstitutional based on developmental science about adolescent risk-taking behavior.