Of all the reasons a beloved professor could be leaving the college where he has taught for the last 20 years, the one for Kent Gramm’s departure is peculiar: He is getting divorced, the college demands an explanation, and he refuses to give one.

The students stood in a circle on the campus quadrangle at the University of Chicago and held slender white candles as they remembered a gentle graduate student from Senegal who was killed early Nov. 19, weeks before he was to receive his doctorate.