The federal government repays states some of the cost of incarcerating undocumented immigrants through the State Criminal Alien Assistance Program.

Criminal aliens have consistently made up about 25 percent of the federal prison population since 2001, according to the study.

The study comes as the immigration debate heats up on Capitol Hill and the White House. President Obama ramped up efforts this week, hosting meetings with key business, faith and political officials on the issue. And Rep. Luis Gutierrez (D-Ill.), the head of the Congressional Hispanic Caucus's immigration task force, is trumpeting the need for immigration reform in speeches across the country. 

Meanwhile, Rep. Steve King (R-Iowa) used the study to back his push for a fence and a wall that runs along the U.S.-Mexico border as a way to stop people from coming into the country illegally.

Nearly 70 percent of the criminal aliens in federal prisons, and 66 percent in state prisons, were born in Mexico, the report found. About five percent are from the Dominican Republic, and five percent from Colombia.

“We have to secure our southern border with a fence, a wall and a fence,” said King, who sits on the House Judiciary Committee’s Immigration, Citizenship, Refugees, Border Security & International Law subcommittee.

“That would drastically reduce the ability of criminal aliens to enter the United States, providing needed relief to overburdened state prison systems and to taxpayers. We also have to do a better job of removing criminal aliens who are apprehended.”

Based on a 1,000-person sample of the criminal alien population, the study found that each non-U.S. citizen in prison had, on average, been arrested seven times over the course of their lives.

“About 50 percent of the criminal aliens in our study population were arrested at least once for either assault, homicide, robbery, a sex offense, or kidnapping,” the study reads. “About half of the criminal aliens were arrested at least once for a drug violation.”

Nearly half of the people – 173 of the 399 – that the Justice Department convicted of crimes related to international terrorism were, at the time of charging, non-U.S. citizens with or without legal immigration status, the report found.