Columbia University remained on edge Wednesday following the Immigration and Customs Enforcement arrest of Mahmoud Khalil, a green card–holding recent graduate who helped lead the pro-Palestinian protests that roiled the campus last spring. A federal judge in New York ruled Tuesday that Khalil could not be deported, but following a procedural hearing on Wednesday, the judge said he will remain in ICE custody in Louisiana for now, CNN reported.

Hundreds of people took to the streets of Manhattan to protest Khalil’s detention; police arrested 12 protesters outside City Hall Park Tuesday night, charging 11 with disorderly conduct, The New York Daily News reported.

Meanwhile, faculty at Columbia warned other student protesters to be careful. Stuart Karle, a First Amendment lawyer and adjunct professor at Columbia Journalism School, advised students who are not U.S. citizens to avoid publishing opinions that could attract the attention of the Trump administration, The New York Times reported.

“If you have a social media page, make sure it is not filled with commentary on the Middle East,” he told students and faculty gathered in Pulitzer Hall.

“Nobody can protect you,” journalism school dean Jelani Cobb added, according to the Times. “These are dangerous times.”

During a news briefing Tuesday, White House press secretary Karoline Leavitt said the Trump administration was using intelligence gathered by the Department of Homeland Security to identify people who participated in campus protests, CNN reported. She accused Columbia of holding back information.

“Columbia University has been given the names of other individuals who have engaged in pro-Hamas activity, and they are refusing to help DHS identify those individuals on campus,” Leavitt said. “As the president said very strongly in his statement yesterday, he is not going to tolerate that and we expect all of America’s colleges and universities to comply with this administration’s policy.”

Last week, the Trump administration canceled $400 million in grants and contracts over what it claimed was Columbia’s “continued inaction” and failure to protect Jewish students.

Columbia’s interim president, Katrina Armstrong, released a statement Wednesday reiterating her guiding principles. She wrote, “A great institution, and particularly a great university, depends upon an unwavering commitment to following fair and just processes, no matter the internal and external pressures.”