Agents told him his student visa was revoked. But he had a green card. Agents then said that was revoked too. Mahmoud Khalil outside the gates of Columbia University’s campus on April 30, 2024. Photo by USA TODAY Network via Getty Images On Saturday, Department of Homeland Security (DHS) officers detained Mahmoud Khalil – a recent Columbia University graduate who helped lead the Gaza solidarity encampment – at his New York City home, an apartment building owned by the school, says advocates....