Ms. Stefanik, a Republican congresswoman and staunch ally of President Trump, abruptly ended her bid to unseat Gov. Kathy Hochul and said she would not seek another House term.

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.