Student negotiator Mahmoud Khalil is on the Columbia University campus in New York at a pro-Palestinian protest encampment on April 29, 2024. (AP Photo/Ted Shaffrey, file) NEW YORK — A prominent Palestinian activist who helped lead Columbia University’s student encampment movement was arrested Saturday night by federal immigration authorities who claimed they were acting on a State Department order to revoke his green card, according to his attorney. Mahmoud Khalil was at his university-owned apartment blocks from Columbia’s Manhattan campus when several Immigration and Customs Enforcement agents entered the building and took him into custody, his attorney, Amy Greer, told...