The Department of Homeland Security Office of Inspector General's report shows that ICE released 600 "criminal aliens" in February 2013, Fox News reports.
The Immigration and Customs Enforcement releases came from jails across the country as part of an effort to cut the number of prisoners because of a budget shortfall.
More than 2,200 total aliens were released between Feb. 9 and March 1, 2013. Initial reports showed that 629 had criminal convictions, though that number was later lowered.
"It is baffling how an agency charged with homeland security and immigration enforcement would knowingly release hundreds of illegals with criminal histories. In this single action, ICE undermined its own credibility, the rule of law, and the safety of Americans and local law enforcement," said Oklahoma Sen. Tom Coburn.
Coburn and Arizona Sen. John McCain requested the investigation.
Most of those with criminal convictions were classified as nonserious Level 3 crimes, the report said. But many were required by law to be kept in custody, and ICE leaders did not require local field offices to keep track of those released.
Many ended up being re-detained, including 24 of the 34 Level 1 detainees and 30 of the 80 Level 2 detainees.
The IG report also noted that ICE is required by law to maintain no more than 34,000 detainees at a time, though it was overseeing 35,000 when the releases were made.
The report comes as the agency struggles with tens of thousands of unaccompanied children from South America who have flooded the southern border seeking what they believe will be permission to stay in the country legally.
Texas Gov. Rick Perry, unhappy with the Obama administration's response, has stationed 1,000 National Guard members along the border and has sent Texas Rangers and Department of Public Safety officials to help.
On Wednesday, Perry told Fox News Channel's "Your World with Neil Cavuto"
that in the five weeks since his surge began, apprehensions in the area have fallen by 56 percent.
He said more could be done if the Federal Aviation Administration would allow the state to use unarmed drone aircraft to scout the area to see where agents should be deployed.
In Arizona, Maricopa County Sheriff Joe Arpaio,
who has had his own battles with the Obama White House, told Cavuto his patience is running out.
He said 3,000 of those in his jails are in the United States illegally. Of those he turns over to ICE, 35 percent keep coming back.
Arpaio told Cavuto he has sent a third letter to Secretary of Homeland Security Jeh Johnson requesting information, but "They always come back with a Mickey Mouse form letter."
Today, he said, he will be talking to the Inspector General for Homeland Security.
"If the IG doesn't come down here, then I'm going to ask Congress to look into it," he said. "I'm tired of the smoke and mirrors and them conning me."
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