Over the last decade, more than 30 district attorneys nationwide, many who consider themselves part of a new wave of prosecutors more interested in fair play than in a stack of guilty verdicts, have established conviction-integrity units. The standalone teams of lawyers and investigators delve into an office’s past cases, hunting for people wrongfully convicted of a crime.

But the practice—which affects the handful of cases in which someone truly innocent went to prison—offers limited redress, functioning more as an emblem of a cultural shift than a broad righting of wrongs. The conviction-review unit in Brooklyn, New York, considered one of the most effective in the United States, has identified just 23 wrongful convictions over the past several decades.

None of these conviction-review units have undertaken the far more ambitious task of examining cases where the conviction might be sound but the punishment doesn’t fit the crime. That would mean poking into the sentences sought by a previous generation of prosecutors whose reflexive stance, for decades, was often to seek maximum charges carrying hefty terms behind bars. “It might open the floodgates to reviewing thousands of sentences,” said Steven A. Drizin, a law professor at Northwestern University and an expert on wrongful convictions, who said he supports sentence reviews.

Despite the daunting undertaking, the idea is starting to gain traction. In Philadelphia, where former civil-rights attorney and public defender Larry Krasner was recently sworn in as district attorney, staffers are making plans for a sentence-review program, likely the first of its kind in the country. Nationally, nearly two dozen newly elected prosecutors are working with an advocacy organization called Fair and Just Prosecution to implement their own sentencing-review procedures in the coming year, said Miriam Krinsky, the group’s executive director and a former longtime federal prosecutor.

Such a massive undertaking is, like many of the ambitions of this new breed of prosecutors, far easier said than done.

Normally, courts allow a prosecutor to seek resentencing only in limited circumstances, such as when new evidence arises or when legislators pass a new sentencing law that needs to be applied retroactively. For example, Maryland in 2016 revised its mandatory minimum sentences, with a clause allowing judges to use those changes to reduce the time that then-current prisoners were serving.

Sometimes, a prisoner can be rewarded with a reduced sentence for cooperating in a police investigation. The compassionate-release process also lets corrections agencies and courts reduce sentences retroactively, usually when the prisoner is gravely ill.

But there is no mechanism in many states for requesting a new sentence for a current inmate simply because a newly elected prosecutor says it’s in the best interest of justice.

Kevin S. Burke, a Minnesota state judge who was the president of the American Judges Association, said many of his colleagues on the bench would love to revisit old cases in which their discretion was fettered by mandatory minimum-sentence requirements. But they would still need to have a clear reason, grounded in law, for reopening a closed prosecution.

“You have to actually find an error,” he said.

In Philadelphia, Patricia Cummings, head of the conviction-integrity unit, already has a workaround in mind. She said a group within the DA’s office focused on sentencing—which she would likely direct but that still needs staff and funding—could start by looking into first- or second-degree murder cases the office prosecuted in the past.

In Pennsylvania, a conviction on those charges automatically ends in a sentence of life in prison without parole. More than 5,000 of the state’s prisoners are currently serving these sentences, the second-highest number in the nation, and about half are from Philadelphia.

If the unit identifies a case where they believe the facts did not warrant such a harsh sentence, it would ask the trial court to throw out the original conviction and accept a guilty plea on a lesser charge of third-degree murder or manslaughter. Those charges carry much lighter sentences.

“We’re still kicking this around,” said Cummings, who previously ran the conviction integrity unit in Dallas.

Philadelphia’s new project is akin to the recent nationwide review—ordered by the US Supreme Court—of all cases in which juveniles were sentenced to mandatory life without parole. The court ruled that condemning minors, who are by nature impulsive and less cognizant of the consequences of their actions, to an entire life behind bars could constitute a form of cruel and unusual punishment. But that ongoing effort was not originally driven by prosecutors.

Another precedent can be found in Seattle, where prosecuting attorney Dan Satterberg has been giving people in prison second chances for the past decade. He and his staff review old cases in which defendants were banished to life in prison for relatively minor crimes, often under the state’s three-strikes-you’re-out law. They then sign on to clemency petitions for some of those prisoners.

Three of the 16 prisoners who were effectively “resentenced” this way have committed new crimes since getting released. But, Satterberg said, “there’s no way to avoid that other than to leave everyone in prison forever.”

“I think a prosecutor has a continuing obligation to justice, past the sentencing date,” said Satterberg. “We have to be willing to roll up our sleeves, look through the files of old cases, and really…compare them to our contemporary law and practice.”

Most states don’t have such a robust clemency system that prosecutors can use it as a kind of back-door resentencing program. In Pennsylvania, for example, only eight life sentences have been shortened through commutation since 1995. State law requires a pardons board to agree unanimously on any such decision.

That means the mechanism will have to differ by state, said Krinsky, the head of the prosecutors’ group. It may even require lobbying efforts to pass new legislation granting DAs the power to file a special motion for amending a sentence.

Another challenge may be the reaction of crime victims, whose attackers might end up with shorter sentences because of leniency, not innocence. “Reopening the wounds of victims has been a concern of conviction integrity work since it appeared on the scene,” said Cummings, the head of the Philadelphia DA’s unit.

Cummings says her office has nonetheless begun reviewing letters from prisoners who say their original sentences were too harsh and deserve another look.

“If nothing else, even if you don’t ultimately change many sentences, it probably heightens the attitude of people within a prosecutor’s office to be careful when they’re making charging decisions,” said Burke, the former American Judges Association president. “So, at least in concept… more power to them.”