Rosemary Billquist had worked a little late on Wednesday, so by the time she returned to her home in western New York it was already getting dark.

She took her yellow Labrador retrievers, Sugar and Stella, for a walk around 5:30 p.m., while her husband, Jamie, stayed behind at their home in Sherman, N.Y., about 65 miles southwest of Buffalo.

But 15 or 20 minutes later, Sugar and Stella came bounding back without her. They were peering backward, barking with unusual urgency.

“They obviously knew something happened,” Mr. Billquist said in an interview on Saturday night. “And I’m thinking to myself, ‘This isn’t right.’”