At the end of 2015, almost 2.2 million people were incarcerated in American prisons and jails, surpassing the population of New Mexico.

The incarceration rate catapulted in the 1970s and continued to swell over the next 40 years, giving rise to today’s prison reform movement. “Mass incarceration makes our country worse off, and we need to do something about it,” then-president Barack Obama said in 2015.

Many of Obama’s efforts focused on nonviolent drug offenders, mandatory minimum sentences, and private prisons. He’s far from alone in thinking those are the best routes for prison reform, says John Pfaff, AB’97, AM’02, JD’03, PhD’05.

But the conventional wisdom misses the real reasons why the United States is the world’s biggest jailer, argues Pfaff, a Fordham University law professor. His paradigm-challenging new book, Locked In: The True Causes of Mass Incarceration—and How to Achieve Real Reform (Basic Books, 2017), aims to dismantle the drug‑war‑focused “standard story,” as Pfaff calls it, of why our prison population is so high. “Why I push so hard against this common narrative is because actually, in the end, it leads us to embrace solutions that won’t work.”

Pfaff is an economist and lawyer who describes himself as a “prisons and criminal justice quant.” He’s spent years diving into data from the Federal Bureau of Investigation, the Bureau of Justice Statistics, and the National Center on State Courts, seeking to understand the problem and politics of mass incarceration.

The book is jammed with statistics, but a few simple ones help illustrate why Pfaff thinks the standard story falls short.

For instance, drug crimes account for about 16 percent of state prisoners, while violent crimes account for more than half. Violent crimes, Pfaff argues, are the primary driver of the swollen prison rate and a better place to focus reform efforts.

“We’ve convinced people that we can do so much just by targeting drugs that they don’t feel the need to start wrestling with, how do we handle violence?”

Pfaff writes that three things have driven the American prison boom. First, sentencing for violent crimes has grown harsher; second, prosecutors’ power is rarely checked; and third, prison guard unions and politicians can have even stronger incentives to maximize the size of prisons than the for-profit private prisons loathed by reformers.

Pfaff says his findings on prosecutors are the most important in the book, as they get far less scrutiny than police, judges, and prison officials. In fact, he could find no data analyzing prosecutors’ choices until he stumbled upon an obscure data set from the National Center for State Courts.

It was a eureka moment. He saw that between 1994 and 2008, crime reports and the number of arrests fell, yet prosecutors filed more felony cases in state courts.

The probability that a felony charge led to prison time stayed the same (about one in four) under Pfaff’s analysis. Simply by filing more felony charges, prosecutors brought about a 40 percent increase in prison admissions.

Pfaff concludes that prosecutors need charging guidelines similar to judges’ sentencing guidelines—scoring systems that weigh elements in a case so that similar offenders are treated equally. Currently they have “unfettered discretion” over how to handle a case in which, for example, a dozen different statutes might apply.

And he’d like to see more prosecutors representing only cities, rather than counties, so that richer whiter suburbs have less sway over criminal justice in poorer urban areas with larger minority populations.

As for why anyone would want to cut time served for a violent crime, that’s the notion Pfaff says people have most wanted to debate as he’s promoted the book. His thinking on the question is still evolving.

He acknowledges lighter sentencing is a political third-rail in a country like the United States. Reducing sentences for violent crime is “the one part where left, right, or center, it’s a very hard road … to get people to come along with me.”

That’s the case for Vikrant Reddy, a senior research fellow on criminal justice reform at the Charles Koch Institute. Reddy calls the book “one of the most important contributions an academic has made in the criminal justice space in many years,” but he’s cautious about fundamentally rethinking punishments for violent crimes. “For very serious violent offenders, the sentences are going to be long and probably need to be long,” Reddy says.

Pfaff thinks long sentences haven’t worked as a deterrent and aren’t cost efficient. He favors shifting money from prisons toward interventions proven to prevent violence in the first place. For instance, studies show that CeaseFire, a Chicago program working to break cycles of violence and retaliation, reduced shooting rates. (The program’s funding was cut in 2015—right before gun violence skyrocketed.)

Elsewhere, Pfaff sees an all-too-common urge in prison reform measures to balance shorter sentences for nonviolent offenses with harsher punishment for violent ones, as South Carolina did in a lauded 2010 reform bill.

None of this is to say that Pfaff believes ending the drug war is a bad idea. He’s for it, even if he thinks it’s a relatively small contributor to the incarceration rate.

He takes heart, too, in the recent bipartisan trend in prison reform that’s coalesced around the standard story. Some in the conservative industrialist Koch brothers’ orbit have teamed with liberal groups like the American Civil Liberties Union to combat mandatory minimum sentences, earning a shout-out from Obama in that 2015 speech.

Pfaff thinks the election of tough-on-crime Donald Trump won’t make much difference to the prison reform movement. If he’s right about what’s putting people in prison, trying to change legislation and executive action at a national level won’t be as effective as reaching out to the thousands of prosecutors across the country and convincing them to change.

Pfaff has plenty of ideas he’s willing to share with reformers of all political stripes. He hopes his book will help them unite around new, more effective strategies to reduce the prison population—though he acknowledges it won’t be simple. “I understand that you don’t turn our system around on a dime. You have to work your way into this,” he says. “Ironically, drugs is the gateway policy issue to reform.”