The parents of the suspect in the Brown and M.I.T. killings had not seen or heard from him since he left Portugal to enroll at a graduate program at Brown more than two decades ago.

Emergency authorities across the region urged people to stay home, and a utility company cut off power to 100,000 of its customers near Denver.

A Reddit user provided information that helped identify Claudio Manuel Neves Valente as the suspect not only in the campus shooting but also in the murder of an M.I.T. professor.