»Highest US court forbids death penalty for children«

Now the Supreme Court has ruled that juveniles may not be sentenced to death. Justice Anthony Kennedy wrote the majority opinion and noted that the trend among states was to abolish the practice of imposing the death penalty on juvenile criminals and said, "Our society views juveniles ... as categorically less culpable than the average criminal."
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The Court went on to point out three differences between juvenile and adult offenders:

Juveniles' susceptibility to immature and irresponsible behavior means "their irresponsible conduct is not as morally reprehensible as that of an adult." Their own vulnerability and comparative lack of control over their immediate surroundings mean juveniles have a greater claim than adults to be forgiven for failing to escape negative influences in their whole environment. The reality that juveniles still struggle to define their identity means it is less supportable to conclude that even a heinous crime committed by a juvenile is evidence of irretrievably depraved character. [citations omitted]
Because 'Capital punishment must be limited to those offenders who commit "a narrow category of the most serious crimes" and whose extreme culpability makes them "the most deserving of execution."' and because of the diminished culpability for these three reasons, the Court concluded that the death penalty could never apply to juveniles.

The Court also noted the overwhelming international opinion against the juvenile death penalty and that "the United States is the only country in the world that continues to give official sanction to the juvenile death penalty." The majority points out that while international opinion "is not controlling" it is useful in affirming what the Court had already decided.

Alarmed by reports that gun homicides have nearly tripled since 1983,248 several States have enacted transfer provisions for juveniles who commit offenses with firearms. In Indiana, Mississippi, and Oregon, juveniles who violate certain firearms laws must be prosecuted as adults. Illinois mandates criminal prosecution of juveniles age 15 and older who violate the State's gun-free-school-zone laws. A juvenile age 14 or older in Arkansas, age 16 or older in Kansas, and under age 18 in the District of Columbia may be transferred to adult criminal court for a violation of those jurisdictions' weapon-free-school-zone laws.