On the night of Jan. 10, someone walked into a home tucked near the forests that blanket Nevada’s northwest border and fatally shot 56-year-old Connie Koontz, the authorities said. Three days later, again under the cover of darkness, someone walked into another Douglas County home about a mile up the road and shot and killed Sophia Renken, 74.

Then, three days after that, Washoe County sheriff’s deputies searched a home about 40 miles farther north on La Guardia Lane. There, they found 81-year-old Gerald David and his wife, Sharon David, 80, both with gunshot wounds; they, too, were dead.

For nine days, law enforcement officials from across the region banded together to both reassure and ready residents who had been shaken by what prosecutors would call “brutal murders.” Lock your doors and windows, the authorities said; turn on outdoor lights; keep your cellphones handy.

By Sunday — the 10th day of regionwide panic — they were able to deliver some calming news: A suspect was in custody; they believed the man, who they have varyingly identified as Wilbur or Wilber Martinez-Guzman, was responsible for all four homicides.