Students marched from Washington Square Tuesday to protest the arrest of Mahmoud Khalil​, a pro-Palestinian activist at Columbia University. Some arrests were made at City Hall.

Mahmoud Khalil, a 29-year-old legal resident of the United States, was arrested and detained by federal agents Sunday, after his green card was revoked by the Trump administration.

When protests over the Israel-Hamas war took root on Columbia University’s campus last spring, Mahmoud Khalil became a familiar, outspoken figure in a student movement that soon spread to other U.S. colleges.