The apocalypse has arrived, at least in Illinois, thanks to Gov. Bruce Rauner’s recent signing of a bill that bars cops and jails from arresting or holding people based on their immigration status. Just ask Immigration and Customs Enforcement.

“This new Illinois law…requires that criminal aliens who are held in local jails be released back into communities, rather than turned over to ICE,” the federal agency charged with enforcing immigration law wrote in a press release issued after Rauner signed the bill Aug. 28. “This is an irresponsible law that will undoubtedly have tragic future consequences at the expense of innocent Illinois residents and visitors.”

To bolster its case, ICE cites the cases of two illegal immigrants who have been incarcerated in the Cook County jail. One is a Mexican man charged with sexual exploitation of a minor. He could be released to the streets, thanks to the new law, warns ICE, which knows the man’s name, where he is located and his next court date. A Guatemalan man with “an extensive criminal history” that includes assault has already been released, ICE says, even though he had previously been deported and ICE had asked the Cook County jail to keep him.

But it’s not that simple. Experts say that illegal immigrants can still be jailed, regardless of state or local laws, if ICE completes the necessary paperwork, which includes getting signatures from judges.

Sheriff’s offices in Cook County and in Sangamon County both say that they’ll incarcerate anyone, regardless of immigration status, if there is a warrant signed by a judge ordering that the person be held. Historically, jails, including the Sangamon County jail, have held people based on detainers issued by ICE, which are requests from a law enforcement agency asking that a person be jailed without a judicial order. That wouldn’t fly if a person was a legal resident of the United States, nor will it fly under the law signed by Rauner.

So, why couldn’t ICE simply go to a judge and get a warrant if the agency wants to jail and ultimately deport a person?

“There’s nothing to prevent that,” answers Michael Kagan, a University of Nevada Las Vegas law professor who specializes in immigration law. “If you know this person is dangerous, why don’t you do what police detectives do all the time and get a warrant? This is not an unusual situation in law enforcement. … The problem is that ICE has been cutting corners. They haven’t set up a system to do what police all over the country do every day, which is get a warrant.”

Even if illegal immigrants aren’t bona fide criminals, ICE could still lock them up pursuant to warrants from judges, according to Kagan. He compares immigration raids to police arresting street-corner drug dealers. In both cases, people are taken into custody without warrants. The difference is, the drug dealer is entitled to a hearing and a judicial finding before he can be jailed beyond 48 hours. Now that Rauner has signed the new law, an illegal immigrant must be afforded the same process.

“Part of what’s going on here is that it is a bit more work,” Kagan says. “This is a judicial check on the government’s power to lock someone up. The government has to fill out some forms to justify their actions. It’s not really a ton of work, but it’s more work than ICE has to do now.”

Typically, Kagan says, the problem comes when illegal immigrants arrested for relatively minor offenses such as driving under the influence are released before ICE can take action. On the other hand, it is possible, at least in theory, for judges to sign warrants authorizing the detention of every known illegal immigrant before they’re arrested for anything. But with an estimated 11 million illegal immigrants in the United States, there simply aren’t enough magistrates, let alone jail cells, to incarcerate everyone.

Jan Ting, who teaches immigration law at Temple University Beasley School of Law in Philadelphia, says that ICE isn’t set up to get warrants. For one thing, he says, ICE attorneys are prohibited from appearing before federal judges and magistrates who have the power to issue warrants, and so ICE would have to rely on U.S. attorneys to obtain warrants on the agency’s behalf. That could prove difficult, he said, because U.S. attorneys may feel as if they have more pressing matters.

“It’s kind of an uphill struggle for any administrative agency to entice the U.S. attorney’s office to represent them in court,” Ting said.

In Sangamon County, the jail has hardly brimmed with illegal immigrants. Since April, ICE has issued detainers to hold nine people in the jail, according to the sheriff’s office. Three already were in custody on charges that included robbery, aggravated DUI, robbery, home invasion, burglary and drug possession.

“Three (detainers) in one month would probably be a little unusual,” says chief deputy Joe Roesch of the Sangamon County sheriff’s office. Roesch says that the sheriff’s office consulted with the state’s attorney’s office and determined that illegal immigrants can no longer be held based solely on a request from ICE.

“We think very highly of the ICE agents: They’re very professional, they’re excellent,” Roesch said. “However, the law changed. We will follow the law. We’ll always honor a warrant.”