AP PHOTOS: Columbia University President Notes Mahmoud Khalil's Absence at Graduation

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.

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.