In court, the trial judge castigated Graham, who had been given a lenient sentence for his first violent offense and chose to "throw it away" after his release.
"Given your escalating pattern of criminal conduct, it is apparent to the court that you have decided that this is the way you are going to live your life and that the only thing I can do now is to try to protect the community from your actions," the judge said.
But some experts say that juveniles can change.
"I believe that kids are just less responsible then adults, and we can't hold them to the same standards of criminal culpability," said Laurence Steinberg, a professor at Temple University in Philadelphia.
"They are worse at making decisions, they are more easily coerced by others, and they have more trouble controlling their impulses," he said.
Steinberg provided information for legal briefs on behalf of both Graham and Sullivan.
Because the United States is the only country in the world that imposes life without parole for juveniles, the case brings up the thorny question of whether the justices should look for guidance from international law when considering the U.S. Constitution.
Justice Antonin Scalia has long been a critic of such a use of foreign law. Other more liberal justices have stressed that there is simply no harm in looking to see how other countries have dealt with difficult issues.
In Roper v. Simmons, the 2005 decision striking down the use of the death penalty for juvenile offenders, Kennedy infuriated some conservatives by writing, "the opinion of the world community, while not controlling our outcome, does provide respected and significant confirmation of our own conclusions."
A decision is likely by early next year.