Cook County Board President Toni Preckwinkle on Thursday defended an ordinance that frees some inmates wanted by immigration authorities. Instead of reconsidering the measure, she asked for a study to identify better ways for the county’s judges to set bail in criminal cases.

The ordinance, passed in September, bars compliance with Immigration and Customs Enforcement requests that certain inmates remain in the county’s jail up to two business days after they have posted bond or completed their court cases. The requests, known as detainers, gave ICE time to pick up the inmates for possible deportation.

Last week a letter to Preckwinkle from ICE Director John Morton said the ordinance “undermines public safety in Cook County and hinders ICE’s ability to enforce the nation’s immigration laws.”

Morton’s letter says ICE has lodged detainers against more than 268 Cook County inmates since the ordinance passed. It says the county has not honored any of them, “preventing ICE from considering removal proceedings against all but 15 of these individuals whom we were able to locate independently and arrest following their release into the community.”

The letter also refers to a case that local newspapers have been covering. As the story goes, a Mexican immigrant named Saúl Chávez allegedly killed a pedestrian in a Northwest Side hit-and-run incident last year. Despite a previous DUI conviction, a Cook County judge set Chávez’s bond at $250,000, Preckwinkle’s office says. When Chávez posted the required 10 percent, or $25,000, the jail released him last fall, reportedly disregarding an ICE detainer. Since then, the newspapers add, Chávez has missed his court appointments, leading to a federal arrest warrant.

Preckwinkle on Thursday afternoon said that case “outraged” her but said she was sticking by the ordinance and introducing a board resolution for the county’s Judicial Advisory Council to undertake a six-month study of the bail bond system. The five-member panel, chaired by Illinois Supreme Court Justice Anne Burke, will recommend ways to improve pretrial services so judges can “make better-informed decisions on bond amounts,” a statement from Preckwinkle’s office says.

The release of county inmates should be left to the courts, not immigration officials, Preckwinkle said at a downtown news conference. “It’s the responsibility of the judicial system to determine whether or not someone is a flight risk, a danger to themselves or a danger to society,” she said. “And once the judicial system makes that decision, that should be the end of it.”

Preckwinkle’s stand is getting flak from some County Board members who voted against the ordinance. Commissioner Peter Silvestri (R-Elmwood Park) said he shared her concern about the county’s bond system. But he said the board should allow the sheriff to honor the ICE detainers. “We should return that discretion to the chief law-enforcement officer of the county,” Silvestri said.

ICE took custody of 721 Cook County inmates on detainers in 2011 and 1,665 in 2010, according to Sheriff Tom Dart’s office. The ordinance requires the jail to free such inmates unless the federal government agrees in advance to pay for the extended confinement.

Jesús García (D-Chicago) and other commissioners who backed the measure say the detainers violated inmates’ due-process rights and eroded community trust in local police. A federal court ruling in Indiana last summer said compliance with ICE detainers is voluntary.