A rise in the prosecution of federal immigration crimes — particularly unlawful re-entry — has changed the face of U.S. prisons and federal courts.

Between 1992 and 2012, the number of offenders sentenced in federal courts more than doubled. At the same time the number of convictions for unlawful entry increased 28 fold, according to a recent study by the Pew Research Center.

The report received scant attention, but it could have political implications in the ongoing debate over immigration reform. Last month, President Obama ordered a review of immigration enforcement policies amid growing pressure from Democrats and Latino leaders.

In 1992, Latinos made up 23 percent of offenders sentenced in federal court. By 2012, that share had grown to 48 percent. Hispanics accounted for 48 percent of sentenced federal offenders in 2012, the single largest racial or ethnic group represented. In 2012, 92 percent of unlawful re-entry offenders were Hispanic, the report found.

Among unauthorized immigrants sentenced in federal courts in 2012, 68 percent were convicted of "unlawfully entering or remaining in the U.S.," meaning they have entered or attempted to enter the U.S. illegally more than once.

Before 2005, U.S. Border Patrol routinely allowed immigrants apprehended at the border to voluntarily return to Mexico without penalty. Since 2005, the Border Patrol reduced its voluntary returns and began employing more stringent methods, such as criminally charging immigrants and increasing the use of what is known as expedited removals, which do not require judicial review, the report found. Some of the prosecutions have taken on an assembly line-like approach through a program called "Operation Streamline," which allows federal authorities to charge and prosecute up to 40 unauthorized immigrants at a time with unlawful re-entry.

The report makes no recommendations but provides a template for debate about the effectiveness — and cost — of current immigration enforcement.

Mark Brunswick • 612-673-4434