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

Claire Shipman, the university’s acting president, noted the absence of Mahmoud Khalil, a graduate who continues to be detained by immigration authorities.

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.