Editorial: Singles: Editorial-Singles-14

Cambridge, MA., April 20, 2013: MIT students gather at a memorial for slain MIT police officer Sean A. Collier in front of the SATA Center on the MIT campus where he was killed. Photograph by Evan McGlinn for The New York Times.

Cambridge, MA., April 20, 2013: MIT students gather at a memorial for slain MIT police officer Sean A. Collier in front of the SATA Center on the MIT campus where he was killed. Photograph by Evan McGlinn for The New York Times.