A pair of teenagers walked up to a security guard in a New Orleans East apartment complex on a September night in 2010, scheming to rob him of his weapon.

The guard wouldn't hand it over and took off running. Sixteen-year-old Anthony Davis shot the guard as he ran. The guard survived, but Davis died when a single shot squeezed off by his friend, 15-year-old Jeremy Burse, ricocheted and struck him in the heart.

A jury convicted Burse of second-degree murder. A judge sentenced him to spend the rest of his life in prison with no possibility of release except in death or by governor's pardon.

For those, like Burse, convicted of murder for killings committed before their 18th birthday, such sentences should be "rare and uncommon," the U.S. Supreme Court has ruled twice in the last five years, and reserved only for those who exhibit "such irretrievable depravity that rehabilitation is impossible."

Despite those Supreme Court rulings, defense attorneys and advocates for juvenile defendants say, courts in Louisiana have continued to impose such sentences on young men convicted of murder for crimes committed as juveniles at remarkably high rates.

As state lawmakers mull a pair of bills that would restrict how the sentences are imposed on juvenile defendants, advocates for broader reform point to the clip at which that "uncommon and rare" sentence is being handed down in Louisiana as evidence the current system is failing to identify the worst of the worst.

No comprehensive tally exists of juvenile murder cases sentenced since 2012, when the Supreme Court issued its ruling. But a review of 23 cases in the state of juveniles convicted of murder — all boys who killed between the ages of 15 and 17 — shows 65 percent received life without parole sentences.

The Louisiana Center for Children's Rights, an advocacy group that tracks such cases, claims the rate may actually be over 80 percent.

"That obviously contradicts the court mandate that it be the rare and uncommon case in which that sentence is imposed," said Aaron Clark-Rizzio, the nonprofit's executive director. "I think that is the most troubling aspect of how the (U.S. Supreme Court) decision has been implemented in this state."

A bill sponsored by state Sen. Dan Claitor, R-Baton Rouge, would limit life without parole sentences to only those juveniles convicted of first-degree murder. Claitor's bill also provides parole eligibility after at least 30 years in prison for roughly 300 inmates sentenced to life without parole prior to the decision.

Clark-Rizzio, whose group has been lobbying to abolish life without parole sentences for juveniles in Louisiana, said the grim upbringings and tough environments that shaped many of the teenagers charged with murder — as well as a wide array of research on juvenile brain development — suggest it's incredibly hard to identify which young convicts might radically change their lives in the coming decades.

Clark-Rizzio and others raise the question of whether a judge — evaluating a teenage defendant within a couple of years of the killing — can determine whether the young killer is "irredeemably depraved." Claitor, a former prosecutor, called that challenge the "conundrum" of trying to fit Louisiana law to the Supreme Court's mandate. "How do you identify the worst of the worst on the front end?"

"Ordinarily, you need some passage of time to figure out if they're really the worst of the worst," Claitor said. "It doesn't make the crime not as awful. It just means the person might not be as awful as we once thought."

For those serving life sentences, the ability to seek parole doesn't provide any guarantee they'll leave prison before their deaths. The Department of Corrections lays out more than a half-dozen other requirements inmates must meet — including educational coursework, disciplinary standards and a low score on the department's risk-assessment tool — before they can be considered.

The state's parole board already denies parole to more than half of those whose cases are considered — a rate that's almost certain to drop if the board, which currently considers parole applications from those convicted of less serious crimes, begins reviewing the cases of convicted murderers for potential release. In Missouri, for instance, the state's board granted parole to only 13 percent of lifers whose cases they reviewed between 1991 and 2013, according to a recent report from The Sentencing Project, a research and advocacy group, and a quarter of which later saw that decision reversed.

In a 2012 ruling in Miller vs. Alabama, in which the court considered the cases of two convicted murderers who were both 15 at the time of their crimes, the U.S. Supreme Court declared that automatically imposing a life without parole sentence on juveniles amounts to "cruel and unusual punishment," ruling that judges must consider a wide range of factors — from mental illness and evidence of peer pressure from older criminals to history of abuse and educational struggles — before denying a juvenile defendant convicted of murder any opportunity for parole.

In response, the Louisiana Legislature quickly amended state law to require sentencing hearings for juveniles convicted of first- or second-degree murder for a judge to consider such evidence before determining whether that particular defendant is among "the worst offenders and the worst cases."

But exactly how those hearings should be conducted — and what findings a judge must make before imposing a life without parole sentence — has remained a point of dispute in the years since.

The amount of evidence presented during sentencing hearings has varied considerably among cases, said Carol Kolinchak, an attorney and the trial-level compliance officer for the Louisiana Public Defender Board who compiled guidelines for public defenders on how to prepare for sentencing hearings that call for extensive background investigations and expert testimony. In some cases, Kolinchak said, judges have imposed the sentence after only a "perfunctory review."

Public defenders, who represent the vast majority of defendants in these cases, say their dire financial position means they lack the resources to mount the intensive investigations and hire the experts needed to present an adequate defense.

"This is essentially a mandate for public defenders with no funding for it," Jay Dixon, the state public defender, told a committee of lawmakers last week. Dixon estimated the statewide cost of adequately preparing for such hearings would be in the millions of dollars.

An Orleans Parish judge in February cited a funding crisis at the local public defenders office before ruling out a sentencing hearing and giving Joseph Morgan, who was 16 when he gunned down another teenager outside a New Orleans club, the possibility of parole.

"The utter failure of the Louisiana Legislature to provide funding for indigent defense cannot be a bar to the constitutional rights … of indigent juvenile defendants," Criminal District Court Judge Arthur Hunter wrote in a six-page decision.

In Jefferson Parish, a defense attorney for convicted murderer Dexter Allen argued repeatedly that a sentencing hearing should be put off because he lacked funds to present evidence of possible mitigating factors in Allen's childhood before sentencing. Those appeals — including a last-minute emergency writ with the state Supreme Court to put off the hearing — were denied, and a judge sentenced Allen to life without parole on Friday.

"There’s no way a higher court is going to look at what I did today and say, 'Yes, Mr. Matthews did an effective job as counsel,'" Allen's attorney, Jerome Matthews, told the judge during closing arguments in the sentencing hearing.

District attorneys have opposed efforts to abolish the sentence altogether for juveniles convicted of murder, pointing out the U.S. Supreme Court's decision clearly allows life without parole in some cases. Hillar Moore III, the East Baton Rouge district attorney, said killers who represent "the worst of the worst" shouldn't be offered any shot at parole.

But how that sentence is imposed also appears to vary among parishes in the state. East Baton Rouge juries have convicted two people of murder for crimes committed as juveniles since the Supreme Court's decision in 2012. Michael Louding, convicted of first-degree murder, received life without parole. G'Quan Baker, convicted on three counts of second-degree murder, will be eligible to apply for parole after serving at least 35 years.

Orleans Parish has seen far more cases: In nine cases where judges held hearings to consider whether to impose the sentence reviewed by The Advocate, only three defendants received the right to petition for parole. One of those given an opportunity for parole, Charles "Chuck" Carter Jr., who went on a bloody armed robbery spree at 17, also received an extra 362 years in prison from an Orleans Parish judge who declared him "utterly evil" and "the worst of the worst."

Chris Bowman, an assistant district attorney and spokesman for the Orleans Parish District Attorney's Office, pointed to the city's high homicide rate when asked about the frequency with which judges have imposed the sentence, saying New Orleans is dealing with a "unique violent crime problem." He added that other defendants charged with murder have pleaded guilty to lesser charges like manslaughter before trial.

Ben Cohen, an attorney with the Promise of Justice Initiative in New Orleans, said the high rates at which juvenile defendants are being sentenced to life without parole suggests the courts in Louisiana aren't capable of fairly weighing a juvenile's capability of being redeemed.

"It's always expedient for a judge or prosecutor — an elected official — to insist on the most severe punishment," Cohen said. "That's why it's dangerous to expect a judge to do what's right."

It also raises the possibility that, without action by the Legislature to limit the use of the sentence, Louisiana may once again find itself in front of the U.S. Supreme Court for failing to adequately implement the Miller vs. Alabama decision, said Mark Plaisance, the Lafourche Parish public defender.

"The argument would be very simple: Louisiana did not get the memo," Plaisance said. "I can't tell you at the end of the day how they would rule, but I certainly think it makes a damn good argument."

Follow Bryn Stole on Twitter, @BrynStole.