Study after study has shown that black men do more time in jail than white men who commit similar crimes — an entrenched racial disparity in the nation’s justice system that Attorney General Eric Holder has decried as “shameful” and unacceptable.

But a new study finds that a previously ignored factor has an even larger impact than race on whether and for how long a person will go to jail: U.S. citizenship.

Immigrants who lack citizenship are four times more likely to be sent to jail than U.S. citizens who committed the same crimes, according to a study of federal sentencing data to be published in the American Sociological Review this month. Once they’re in jail, immigrants serve two to four months longer than the average citizen convicted of the same crime.

This sentencing gap between citizens and noncitizens is even larger than ones found between black defendants and white defendants, according to Michael T. Light, the study’s author and an assistant professor of sociology at Purdue University. Lacking citizenship appears to be worse news for a defendant than his or her race. A white noncitizen faces more jail time, on average, than a black U.S. citizen convicted of the same crime, the study found.

Citizenship “appears to trump race and ethnicity when determining punishments for those who violate U.S. law,” the study concludes. The effect was starkest for undocumented immigrants, but even legal immigrants faced significantly longer sentences than citizens convicted of the same crimes, regardless of their race. Most of the sentencing disparity between Hispanics and whites could be explained by the higher percentage of noncitizens in the Hispanic group, the study found.

The sentencing gap appears to have grown with the size of the noncitizen population of the country, which has expanded to about 38 million people. Noncitizens make up more than a quarter of the country’s federal inmates. They are generally deported once their sentence is up. Most noncitizens in prison are serving time for federal immigration crimes, but the researchers examined only non-immigration offenses committed by noncitizens to be able to compare them to the same crimes committed by citizens.

Story continues

It’s unclear why noncitizens are punished more severely by the courts. The Supreme Court has repeatedly held that undocumented immigrants have a right to due process — and legal immigrants should be treated the same by the law. Light theorizes that the disparity might be a reflection of public opinion. A majority of Americans say in polls that they believe immigrants are likely to cause higher crime rates. This perception of higher criminality could result in harsher punishments.

Holder has called racial disparities in sentencing "unacceptable" and has launched a series of reforms aimed at rolling back mandatory minimums for drug crimes in order to combat them. It’s unclear if these reforms would help close the citizen-noncitizen gap as well, Light said.

“Any policy aimed at avoiding unwarranted disparities is a good thing,” he said. “It’s not that we shouldn’t focus on race and ethnicity, but that we should also include nationality.”