Updated February 17, 2022 at 12:15 PM ET

The Justice Department should reconsider how it punishes juveniles accused of homicide, a coalition of former federal, state and local prosecutors wrote in a letter released on Thursday that urged limiting the use of sentences of life without parole.

The group wants Attorney General Merrick Garland to agree to seek life without parole sentences only in the rarest of cases, where juveniles are "incapable of change." In all other instances, it said, federal prosecutors should ask for no more than 30 years in prison.

"Violent crime warrants proportionate punishment," said the letter from the Institute for Constitutional Advocacy and Protection at Georgetown Law Center. "But justice demands that any such punishment reflect an offender's youth and capacity for rehabilitation."

Most adults serve a median of 20 years in federal prison and 17 1/2 years in the state system, the advocates said.

The letter, signed by former Justice officials from both Democratic and Republican administrations, called for creating a unit to review all requests from federal prosecutors for life sentences for people under age 18 and requiring sign-off from the attorney general to proceed.

The department should also review the cases of juveniles already serving federal life sentences and evaluate whether they can be released if they're capable of rehabilitation, the letter said. That would apply to fewer than a dozen people, according to court filings in a related case.

A Justice Department spokesperson said the DOJ has received the letter and is reviewing it.

In a stream of cases going back more than 15 years, the Supreme Court has said that juvenile offenders are different than adults who break the law, because of their developing brains, vulnerability to peer pressure and other factors.

In 2005, the high court ruled capital punishment is unconstitutional for juveniles. Five years later, the court said life without parole sentences for juveniles are unconstitutional in cases that don't involve murders. Last year, a divided court found that sentencing judges aren't compelled to determine if a juvenile is incorrigible before imposing a life without parole sentence.

But the Georgetown group is pushing the Justice Department to go further, at least in a tiny number of cases where federal prosecutors charge juveniles with murder.

Among them is Riley Briones Jr., who studied for his GED, helped younger inmates, and developed a "spotless" record in prison. Late last year, a panel of the U.S. Court of Appeals for the Ninth Circuit affirmed his life sentence. But Briones, who was convicted of murder on an Indian reservation, is asking the full appeals court to hear his case. Briones said he was abused by his father and that he acted only as a getaway driver in the murder of a Subway sandwich shop clerk in 1994.

Copyright 2023 NPR. To see more, visit https://www.npr.org.