The Department of Justice made a landmark decision last week when it announced it would direct the Bureau of Prisons to let its contracts with private prison companies lapse.

But last week’s change in policy left the U.S. Marshals Service untouched, even though that agency is also under DOJ control and keeps nearly as many people locked in privatized jails as the Bureau of Prisons.

The U.S. Marshals Service is the country’s oldest federal law enforcement agency, acting under the authority of the federal courts. They provide courthouse security, run the Witness Protection Program and detain suspects facing federal criminal charges. When other federal agencies, like the Drug Enforcement Administration or the Border Patrol, arrest people for federal crimes, they hand the suspects off to the Marshals Service. Those convicted with short sentences often remain in the Marshals’ custody instead of being transferred to the Bureau of Prisons.

A Shifting Mission

Ross D. Franklin/AP

Over the last decade, the Marshals Service has seen its responsibilities change sharply, shifting toward the prosecution of routine immigration offenses that were historically punished with deportation alone. The crimes of illegal entry and re-entry accounted for about half of the criminal cases referred to the U.S. Attorney’s Office in 2013, the most recent year for which the Bureau of Justice Statistics has compiled data.

As the number of people funneled into its custody over immigration offenses ballooned, the Marshals Service turned to private prison contractors to expand its detention capacity, according to Carl Takei, a staff attorney with the ACLU’s National Prison Project.

“The chief impact of this has been to spend the Department of Justice’s money to hold people in criminal custody for immigration offenses and line the pockets of private prison companies who are engaged in that detention,” Takei told The Huffington Post. “It’s not connected to any of the Justice Department’s stated prosecutorial priorities.”

The average daily detention population under the U.S. Marshals Service’s custody nearly tripled to 59,542 in the two decades from 1994 to 2013, according to data obtained through a Freedom of Information Act request by the ACLU and shared with HuffPost. Thirty-one percent of them, some 18,477 people on an average day, slept in beds provided by private contractors in jails run as for-profit businesses. That figure has swelled from 21.5 percent since 2006, the first year in which the ACLU’s data set provides a full accounting of its use of private prison contractors.

By contrast, the 22,660 prisoners locked up by the Bureau of Prisons in privatized beds amounted to 12 percent of the total prisoners in their custody.

The Marshals Service referred questions about its use of privatized jails to the Department of Justice. DOJ referred HuffPost back to last week’s memo, which doesn’t mention the Marshals Service.

HuffPost counted at least 14 Marshals Service contracts with privatized jail facilities listed on the agency’s website ― one more contract than the Bureau of Prisons. The country’s largest private prison contractor, Corrections Corp of America, runs seven of them. The second-largest private prison company, GEO Group, runs the other seven.

The Marshals Service may have contracts with more privatized jails. Three of the contracts between the agency and private corporations counted by HuffPost didn’t name the company involved in the agreement.

For example, the agreement that allows the Marshals Service to use bed space at Torrance County Detention Center in New Mexico names only the local government as the contracting party. But CCA manages the Torrance facility and the company’s website names the Marshals Service as one of its clients there.

While supporters of prison privatization have contended that private companies can offer the same services for less money, that doesn’t appear to be the case with the Marshals Service. The daily rate it paid to private companies for each detainee they housed through a direct contract averaged $95.27 in 2013, the ACLU data show. The same service cost an average of $69.86 when carried out by a state or local government.

Why The Marshals Service Detains So Many Migrants

ASSOCIATED PRESS The Torrance County Detention Facility in Estancia, New Mexico, is shown in this file photo on Nov. 11, 2000. The Marshals Service pays to use space at the facility, which is run as a for-profit business with the Corrections Corp of America.

Beginning in 2005, immigration offenses became an increasingly large part of the Marshals Service workload. That year, the Department of Justice began implementing Operation Streamline, a plan to prosecute migrants for the little-enforced crimes of illegal entry, a misdemeanor, or illegal re-entry, a felony. Originally pushed by the Department of Homeland Security, the idea emerged as a way to cope with a lack of detention bed space in South Texas.

Since then, immigration offenses have grown to account for 48.3 percent of the federal criminal cases handled by U.S. attorneys in 2013, the most recent year for which data is available from the Bureau of Justice Statistics. Drug offenses came in a distant second, at 19.1 percent.

Virtually all of those who face a federal district judge for immigration offenses are found guilty. About three-quarters of those charged with the felony immigration crime of illegal re-entry ― or crossing into the United States unlawfully after being deported once before ― served jail sentences, averaging 21.6 months, according to the BJS report.

That shift in priorities since Streamline began has made for a skewed system, in which 56.7 percent of those convicted in federal criminal court were Hispanic.

Some lawmakers have applauded the change. U.S. Sens. John McCain and Jeff Flake ― Republicans from Arizona, one of the states where the federal government prosecutes the most illegal entry and re-entry cases ― authored a resolution earlier this year praising Streamline as an effective program that has boosted border security.

But U.S. Rep. Raúl Grijalva, a Democrat from Tucson, called Operation Streamline “cattle call justice” in an interview with HuffPost and said the DOJ should extend the review of its policies to cover the Marshals Service and the Department of Homeland Security, which oversees sees the civil immigrant detention system.

“We keep fattening the calf with immigrant detainees,” Grijalva told HuffPost. “The DOJ has to do something comprehensive to look at the role that these prisons are playing in why we’re not reforming the criminal justice system, why we don’t pass immigration reform.”

“Everyone talks about the need for immigration reform,” Grijalva added. “But as long as we’re feeding this private industry, these private prisons, that’s the source of opposition that’s going to fight us all the way.”