Does a common law practice dating back to 15th century England prohibit the federal government from arresting immigrants in and around courthouses?

That was one of the arguments before U.S. District Judge Jed Saul Rakoff on Wednesday, as the government sought to dismiss a lawsuit by the New York State Attorney General and the Brooklyn District Attorney.

The plaintiffs cited a study finding ICE arrests in and around courthouses shot up by 1700 percent in the first two years after President Donald Trump took office. Lawyers for the state AG’s office told Judge Rakoff this marked a change in policy, which violated the Administrative Procedure Act that governs how agencies make their rules.

Attorney Scott Eisman also said immigrant arrests inside and outside courthouses disrupt judicial proceedings, which are controlled by the state and therefore protected by the Tenth Amendment. He cited a case in Yonkers where an arrest led to a broken glass door at a courthouse, and another that led bystanders to presume someone was kidnapped.

But this is not just a case about state’s rights. Eisman argued that U.S. immigration laws do not override common law privileges dating back centuries, and which prevent any civil arrests in and around courthouses. Immigration enforcement is a civil matter, not criminal.

Assistant U.S. Attorney Rebecca Friedman, however, said references to “arrests” under common law privileges were actually about serving a summons. She said these privileges were intended to grant immunity to people from other states who feared being served while traveling. She also argued that immigrants can be arrested anywhere under the broad powers of the government. Lawyers for the state AG’s office argued those interpretations were too narrow.

Judge Rakoff asked about the limits of common law privileges. At the start of the hearing, he said he was “very surprised” that neither party mentioned common law cases after the 1850s. He also seemed skeptical of the government’s request to dismiss the case, because the location of immigration enforcement can’t be challenged. “That seems pretty extraordinary,” he quipped. Assistant U.S. Attorney Tomoko Onozawa replied that immigrants can sue the government for how they’re treated, for example, if they claim excessive force was used by an officer.

Like a professor pleased by bright students who’d given him new questions he hadn’t considered before, Rakoff ended the hearing by calling the case “fascinating.”

“I have no clear determination yet on many of the questions raised,” he said, adding, “I thought this would be a piece of cake.”

The judge said he needed time to delve into case law and asked both sides to give him their final arguments in writing by December 3rd, with the expectation that he would issue a decision by year’s end.

Beth Fertig is a senior reporter covering immigration, courts, and legal affairs at WNYC. You can follow her on Twitter at @bethfertig.