In all of this, Kennedy’s insights were supported by a variety of recent research suggesting that people are more likely to obey the law when they view law enforcement as fair and legitimate. Tom Tyler, a psychology professor at New York University, has found that compliance with court orders is highest for offenders who perceive that they have experienced a fair process. And in a recent book, “American Homicide,” the Ohio State University historian Randolph Roth argues that throughout American history, the homicide rate has decreased when people trust that the government is stable and unbiased and believe in the legitimacy of the officials who run it. Similarly, the legal scholar Paul Butler argues in his new book, “Let’s Get Free: A Hip-Hop Theory of Justice,” that widespread incarceration in the 1980s and ’90s undermined the legitimacy of law enforcement in the eyes of the affected communities by converting a prison term into something heroic rather than stigmatic.

After Operation Ceasefire, Kennedy turned his attention from gangs to open-air drug markets. He set out to change how the criminal-justice system was viewed from the perspective of the offenders and their communities — and how the offenders and their communities were viewed by the police. As Kennedy told me, “I saw law enforcement believing plausible but untrue things about the communities they police” — namely, that the communities were corrupt and didn’t care about the violence that was destroying them — “and the communities believing untrue things about the police” — namely, that the cops were part of a racist conspiracy to lock up black offenders while overlooking white ones.

To correct what he calls a “corrosive and tragic mistake,” Kennedy came up with the idea of a kind of truth-and-reconciliation commission in which offenders would talk to the police accompanied by the people they trusted the most: their mothers. In 2003, working with James Fealy, the police chief in High Point, N.C., Kennedy arranged some preliminary meetings. Although Fealy had been shocked to learn that the community thought he and his officers were almost as bad as the drug dealers, Fealy, in turn, surprised community members by declaring that no one in law enforcement thought the drug war could be won.

These meetings prepared the groundwork for the strategy that followed. After identifying 16 active drug dealers, Fealy arrested four and then prepared warrants for the other 12 that could be signed whenever the police chose. He then called in the other dealers, nine of whom arrived accompanied by their mothers and other “influentials” like grandmothers, and delivered the following message to them as a group: “You could be in jail tonight. We don’t want to do that, we want to help you succeed, but you are out of the drug business.” The mothers and grandmothers, seemingly impressed by the decision not to arrest, cheered on the police. In subsequent meetings, the “influentials” shouted down naysayers, including a conspiracymonger who accused the C.I.A. of having created the crack epidemic to oppress black people. The drug market in the area dried up.

IN ADDITION TO influencing Judge Alm’s probation reform, Kennedy’s efforts to rethink deterrence have also inspired one of the most powerful recent models for national parole reform, which comes from Tracey Meares, a law professor at Yale. (Unlike probation, which involves a sentence instead of prison, parole involves supervision after part of the prison sentence has been served.) In 2002, Meares, who was then a law professor at the University of Chicago, was asked by the U.S. attorney in Chicago, Patrick Fitzgerald, to analyze how best to address crime in the city. She concluded that they should begin on the West Side, in West Garfield Park and the surrounding area, where rates of murder and gun violence were more than four times the city average. Fitzgerald suggested that they might implement a version of Project Exile, a controversial program in Virginia that sought to deter gun violence by threatening federal prosecutions — and a five-year mandatory minimum sentence — for repeat offenders convicted of illegal gun possession. But Project Exile had experienced only mixed success: federal prosecutors could prosecute only a small proportion of the gun cases submitted by the Richmond police. The threat of a severe sentence was, in effect, something of a bluff.

Meares told Fitzgerald that threats of zero tolerance wouldn’t work because they simply weren’t credible. Instead, Meares argued that law-enforcement officials should concentrate on specific groups of wrongdoers in ways they could accept as both reasonable and fair. Using Operation Ceasefire in Boston as a model, Meares identified everyone who had committed violent or gun-related crimes and had been released from prison and recently assigned to parole. She gathered them in random groups of no more than 20 for call-in sessions in what Meares calls “places of civic importance” — park buildings, local schools and libraries — where they sat at the same table as the police in order to create an egalitarian, nonconfrontational atmosphere. They then heard a version of Kennedy’s three-part presentation. The results of the program were drastic: there was a 37 percent drop in the average monthly homicide rate — the largest drop of any neighborhood in the city. Violent crime in Chicago today is at a 30 year low. “All these strategies are a way of signaling to groups of people that government agents view them with dignity, neutrality and trust, which is the best way of convincing them that the government has the right to hold them accountable for their behavior,” Meares told me.

From Kennedy and Kleiman to Alm and Meares, the judges and scholars developing new deterrence strategies are changing the way we think about parole, probation, gang violence and drug markets. But the strategies also present a rare opportunity to persuade the nation’s policymakers that the most urgent case for prison reform is not only economic but also moral and practical. Yes, it’s an outrage that the United States locks up citizens for so long with such uncertain effect; but it’s also self-defeating, because long sentences give rise to a crisis of legitimacy that can lead to more crime, not less.

A crisis of legitimacy may sound like a huge, perhaps intractable problem, but the tantalizing promise of the new deterrence thinking is that the crisis can actually be solved, practical step by practical step. The relative simplicity of the solutions, it turns out, is at the core of their radical potential.