Monday's developments are rooted in a complex legal history.
In June 2012, the Supreme Court ruled that children under 18 convicted of homicide could no longer receive mandatory sentences of life without parole. Such automatic sentences, the court found, are unconstitutional, violating the Eighth Amendment's prohibition against cruel and unusual punishment. Life sentences for juveniles committing murder are allowable; they just cannot be mandatory.
The court said children cannot be blamed the same way adults can, since juveniles do not fully weigh risks, are prone to peer pressure, and do not possess completely developed brains. The court also said juveniles have "greater prospects for reform" than adults.
The ruling caused confusion, however. While it said that juveniles committing murder could not receive mandatory sentences of life without parole in 2012 and beyond, it did not address inmates already serving such sentences.
In October 2013, the Pennsylvania Supreme Court stepped into the void. It found that the U.S. Supreme Court's ruling could not be applied retroactively. Anyone given a mandatory sentence of life without parole who had exhausted all appeals by 2012 would not fall under the federal ruling, the state court said.
Advocates were troubled by the notion that the year a person was sentenced would determine whether he or she would face life without parole.
"The vagaries of timing should not determine if a juvenile should spend the rest of his or her life in prison with no possibility of parole," according to a Juvenile Law Center statement last year.
The center, along with the Defender Association of Philadelphia, appealed the Pennsylvania decision to the U.S. Supreme Court. Monday's nondecision was the result.
"This is a surprise, and not a very good one," said Bradley Bridge, an assistant defender with the association. "It's puzzling."
Bridge said Pennsylvania had become the third state to say the U.S. Supreme Court ruling is not retroactive. Six states have gone the other way.
Such a split cannot stand for long, said Emily Keller of the Law Center. Bridge agreed, saying it was "intolerable for a citizen of Pennsylvania to be denied relief, while a citizen of Texas [one of the six states that allows the ruling to be retroactive] gets relief. That is not a just result."
At some point, Keller and Bridge said, the U.S. Supreme Court will have to make a ruling that will stand for every state.
Hugh Burns, chief of the appeals unit of the Philadelphia District Attorney's Office, agreed that "it's not fair" that "those who take a life after a certain date get a break others do not." But, he added, "law is all about line drawing."
More important, Burns said, he takes issue with the U.S. Supreme Court's saying that a juvenile's young brain can't determine right from wrong.
"The idea that a person's brain isn't developed to understand that murdering someone is wrong and subject to serious penalty is to me very odd," he said.
Pennsylvania has more than 500 people convicted as juveniles and given mandatory life sentences - 300 of them from Philadelphia, advocates say. The United States is the only country that doles out mandatory life sentences to juveniles. And Pennsylvania has 25 percent of such offenders, advocates say - more than any other state or nation.