Justice Kennedy delivered the majority opinion in a 5-4 decision that reversed the Ninth Circuit. The majority found that the state criminal court that convicted Alvarado had reached a reasonable conclusion that the minor was not in custody for Miranda purposes when he was interviewed. The Court cited a number of factors that indicated that Alvarado was not in custody at the time he was questioned, including the fact that he went to the station voluntarily, was never told he could not leave, was not threatened by authorities, was told the interview would be brief, and was allowed to return home afterwards. According to the Court, Miranda can be distinguished from other cases that require special consideration of age for juvenile offenders.
The majority also stressed the importance of a clear rule for police to apply. Allowing different standards for juveniles would make it more difficult for police to determine when Miranda warnings are necessary.
Though she joined the majority, Justice O’Connor wrote a separate, single paragraph to emphasize her sense that in other cases the age of the defendant could be relevant to the custody determination. She suggested that the failure to consider age could justify reversal in other circumstances. The fact that Alvarado was 17 years old made a difference to her.
Justice Breyer wrote a forceful dissent in which he criticized the majority's characterization of the facts. Justice Breyer framed the issue in the following way:
What reasonable person.brought to a police station by his parents at police request, put in a small interrogation room, questioned for a solid two hours, and confronted with claims that there is strong evidence that he participated in a serious crime, could have thought to himself, "Well, anytime I want to leave I can just get up and walk out?"The dissent said that the involvement of Alvarado's parents suggested that his participation was not voluntary and that a two-hour meeting gave the appearance of custody. The dissent also considered the many ways in which the court system treats juveniles differently, emphasizing that confinement determinations for juveniles should also be treated differently.
You can read the full decision at Cornell's web site.