The U.S. Supreme Court has created a safety net in recent years for juveniles when it comes to the stiffest possible criminal punishment.

Execution is off the table. So is life in prison for juveniles who didn't kill someone. And only in rare cases marked by "irretrievable depravity" can a young murderer be denied a shot at eventual parole, the high court has said.

Those rulings, buttressed by the science of adolescent brain development, left the Louisiana Supreme Court pondering a curious side effect of the high court's decrees as the state court's seven justices weighed the fate of Alden Morgan at a Sept. 8 hearing.

Morgan, now 35, is serving a 99-year sentence without the chance of parole for an armed robbery committed in New Orleans' Garden District in 1998, when he was 17.

He falls under none of the restraints the U.S. Supreme Court set in a spate of decisions over the past decade. Morgan's gun went off as his victims — a couple with their baby daughter — scurried away and Morgan sped off in their burgundy Volvo. No one was hurt.

Morgan argues that his sentence is unconstitutionally excessive, and several of the justices remarked on a conundrum at the heart of the case.

"Isn't it correct, under the law now, that his net punishment is substantially higher than had he been convicted of second-degree murder?" Justice Scott Crichton asked.

"What's the difference between 99 years and mandatory life? Can we discuss that?" Chief Justice Bernette Johnson asked.

"I think you'd have to concede, a 99-year sentence essentially and perversely incentiviz(es) the criminal to actually pull the trigger and commit the homicide," Justice John Weimer added, "because then he's entitled to parole eligibility, but if he doesn't kill anybody, he's not."

The case appears to mark the first time the state's high court has considered how the U.S. Supreme Court's rulings on young killers — based on the notion that their immature brains signal "diminished culpability and greater prospects for reform" — might play out for lesser offenses.

A few of the justices also expressed dismay that, in light of those rulings, Orleans Parish District Attorney Leon Cannizzaro's office offered only one argument: that Morgan is legally out of luck in seeking a reprieve from the sentence that former Criminal District Court Judge Julian Parker handed him in 1999.

Morgan was arrested shortly after the robbery in the 1100 block of Second Street. A police officer tracked him by a cellphone that one of the victims had left in the Volvo, chasing it until the car hit a tree and the officer found Morgan hiding in a nearby shed.

Morgan confessed, saying he had approached the couple as they were putting their baby in the car, demanded the keys, and then "the gun went off, 'Pow!' " as he reached down for the man's wallet on the ground.

The couple later testified at Morgan's trial that he'd kept the gun pointed to the ground as the mother unstrapped the baby from the car seat. They heard it fire as they retreated.

Armed robbery carries a sentence of 10 to 99 years. Following Morgan's conviction, Parker handed him the maximum, finding that "it was Morgan's intent to kill either this child or (the father)," and that he showed no remorse.

The judge, who left the bench in 2014, stood by that sentence after a hearing in which a new attorney presented testimony that Morgan had been placed in three different inpatient programs for mental health problems that included "homicidal and suicidal ideations," the latest coming shortly before the crime.

He'd attempted suicide several times beginning at age 10, was diagnosed with mild mental retardation and also abused cocaine and heroin, according to testimony from his mother and a juvenile probation officer.

"I have heard nothing today," Parker concluded, "that ... would in any way change my opinion of his propensities for violence and his propensities to kill people," according to a transcript.

All of Morgan's appeals, including a petition for federal habeas corpus relief, were rejected. But he filed a new challenge from prison based on the recent U.S. Supreme Court cases, including the retroactive ban on mandatory life sentences for juveniles. The state Supreme Court took up his case last year, assigning the Loyola Law Clinic to represent him.

Loyola law professor Majeeda Snead and law students Ashley Crawford and Meagan Impastato argued that Parker never took into account "mitigating factors of his youth" in sentencing Morgan. 

The U.S. Supreme Court's 2012 decision in Miller v. Alabama requires a judge to consider those factors before sentencing a juvenile killer to life without parole.

Even if he had killed someone, Crawford argued, there was no evidence he was "the worst of the worst," the kind of rare case that warrants life without parole. 

"We've now seen an evolution for how courts are supposed to treat juvenile offenders, and evolving standards of decency require a new review of Mr. Alden Morgan's case," Crawford argued.

But Orleans Parish Assistant District Attorney Christopher Ponoroff noted that Parker heard at least some mitigating evidence about Morgan's troubled youth before sticking to his sentence of 99 years. Ponoroff also argued that "the facts of the crime itself reflect what the U.S. Supreme Court has referred to as 'irreparable corruption.' "

Neither Miller v. Alabama nor Graham v. Florida, the 2010 decision barring life sentences for juvenile offenders not found guilty of homicide, applies in Morgan's case, the prosecutor said.

A few of the justices downplayed the difference, given the near certainty of Morgan dying in prison.

Ponoroff conceded that "in some sense we can, I think, liken it to a life sentence."

"Well, how could you not?" Justice Jeannette Knoll responded.

Justices Crichton and Johnson questioned why the court should wait for another federal court edict to act.

"Is it the position of the Orleans district attorney ... that we should, because this fits under a little narrow hiatus in the law, we should just punt and let the U.S. Supreme Court do whatever they have to do?" Crichton asked.

"Our position is that this case does not fall within any of those other cases, and therefore the defendant is not entitled to raise his issue anew," Ponoroff argued.

"Are you authorized by your office to offer us any alternative to your primary argument, which is, we just deny relief?" the justice asked.

"We do not have any other position or argument, Your Honor," Ponoroff replied.

"Really?" Crichton responded.

Knoll described that position as "such a waste of taxpayer time" and said, "I wish the DA's Office would be a little more practical in their approach to some of these cases."

Snead, the Loyola law professor, said prior court rulings have deemed 35 to 50 years as the appropriate range for a first-offense armed robbery.

The court has yet to rule on the case.

The male victim in the armed robbery, Phillip Spengeman, has since died. Attempts to reach the other two victims were unsuccessful.

Follow John Simerman on Twitter, @johnsimerman.