The Columbia graduate student was supposed to attend the graduation celebration. Instead, he is in immigration detention, caught up in Trump’s crackdown on foreign students.

The head of Columbia University alluded to the detention of Palestinian activist Mahmoud Khalil during a commencement speech Wednesday that drew loud boos and chants of “free Palestine” from graduating students.

Columbia University’s acting president has now faced a massive chorus of boos from this year’s graduating class for the second day in a row, receiving a particular wave of anger on Wednesday while noting the absence of Mahmoud Khalil — a student who would have graduated this week if federal immigration agents had not detained him for peacefully protesting on campus against Israel’s ongoing destruction of Gaza.