Can we release violent criminals from prison without increasing crime? Yes.

Conservative columnist Ross Douthat at the New York Times is worried about mass incarceration in the US — an issue that has united people from the conservative Koch brothers to President Obama's former US attorney general, Eric Holder. But he wonders whether it's possible to address this issue and reduce incarceration without breaking America's 24-year crime-reduction streak, in which violent crime has fallen by 51 percent and property crime by 43 percent.

Douthat first acknowledges that incarceration in America can be truly grisly:

We've been debating criminal justice reform in earnest ever since Ferguson exploded last summer, with policing as the focal point. But our archipelago of prisons, the Dannemora-like places spread around the country, are as much the issue as any abuses by the police.

All told, our prisons house around 2.2 million Americans, leaving the land of the free with the world's highest incarceration rate. And they house them, often, in conditions that make a mockery of our supposed ban on "cruel and unusual" punishment: gang-dominated, rife with rape, ruled by disciplinary measures (particularly the use of solitary confinement) that meet a reasonable definition of torture.

On this point, criminal justice reformers likely agree with Douthat. America currently leads the world in incarceration, its prisons are overcrowded, and some of the conditions and tactics in US jails and prisons are abhorrent. Solitary confinement in particular has been proven by a huge body of research to not just worsen but actually cause mental health problems — yet it's still a common security measure and form of punishment used on inmates, some of whom haven't even been convicted of a crime.

But Douthat points out that to truly reduce incarceration, America will soon have to reduce the sentences of violent offenders as well. That's also correct. According to the Marshall Project's great calculator, even if you released every person in prison for property, drug, and "other" crimes (not something most people would want to do, since car thefts are still bad), you still couldn't reduce the prison population by half — a common goal for reformers. So violent offenders have to be part of criminal justice reform at some point.

Douthat's concern is whether reformers can focus on potentially freeing some of those violent offenders without increasing crime. There are two good reasons to think it's possible: mass incarceration played a small role in the violent crime drop in the past few decades, and current prison sentences are so long they tend to last way beyond a typical person's crime-committing years, anyway.

1) Mass incarceration played a small role in the sharp drop of crime

Brennan Center for Justice

When it comes to incarceration, criminologists generally accept that locking up violent offenders must reduce violent crime to some extent — since it directly keeps a violent offender off the streets. Most criminologists estimate that incarceration explained 10 to 25 percent of the crime drop, although the research on this is ongoing and heavily debated.

But in terms of violent crime, a review of the research from the Brennan Center for Justice concluded that the US was already locking up truly violent criminals in the 1980s — before crime began dropping in the 1990s. So while there must have been some effect, it wasn't big enough to overcome the crime wave of the 1980s. Brennan suggests that something else — most likely a combination of many variables — triggered the big fall in crime that started in the 1990s and has continued through the 2000s.

What's worse, incarceration can also backfire and lead to more crime in the long run. When someone is thrown in prison, he's exposed and connected to all sorts of violent criminals and gangs that he may not have socialized with before. And on a broader scale, pulling large chunks of young men from their communities can lead to the kind of socioeconomic squalor that produces more crime. As Mark Kleiman, criminal justice expert at New York University's Marron Institute, indicated, some research shows adding another prisoner in some states leads to more crime.

But the general evidence suggests mass incarceration played a small role in the crime drop of the 1990s and 2000s. If so, it stands to reason that pulling back incarceration won't increase crime much, either.

2) People age out of crime, so maybe violent offenders don't need to be held in prison for decades

Nikki Kahn/Washington Post via Getty Images

With mass incarceration, it's not just that more people are being thrown in prison, but that people are being thrown in prison for longer.

But this approach keeps people in prison when they're no longer a likely threat to society. The research shows that people are most likely to commit crime in their late teens and early 20s. After that, the chances dwindle — people settle down in their lives and begin more sustainable careers, old age comes with less energy, and older bodies make it a lot more difficult to run around and get in trouble.

In other words, people age out of crime. So letting them out of prison five, 10, or 20 years down the line — instead of 30 or 40 years, or never — likely wouldn't pose a big threat to public safety.

Criminal justice experts have made this claim in the past few years as they've looked for ways to reduce America's enormous prison population. "Crime is a young man's endeavor," Brian Elderbroom, senior fellow at the Urban Institute's Justice Policy Center, told me in December. "It's not surprising that someone who commits a crime at a young age would be a completely different person by the time they're in their 30s."

Now, there are some older inmates who will probably come out of prison and commit more crimes if they don't get any support. That's why some reformers, like Kleiman, have proposed a "graduated reentry" system that eases inmates from prison to the outside world through strong oversight and incentives. For example, an inmate might be allowed more luxury time or autonomy if he can obtain and sustain a job for six months. This has two big benefits for the inmate: he's doing things — like keeping a job — that will help him get a foothold in the real world, and he'll learn how the real world works. (Supporters of this concept acknowledge it's new and will need changes if it's implemented, but the first step, they say, is trying it out.)

So it's possible to reduce the incarcerated population, even violent offenders, without running the risk of more crime. It's not always going to be an easy problem to solve, and sometimes it will require new ideas like graduated reentry. But at the very least, these are ideas that can get some traction and discussion as people on both sides take the problems posed by mass incarceration more seriously.

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