In a statement, Maj. Gen. Walter E. Piatt, senior commander of Fort Drum and the 10th Mountain Division, called Trooper Davis “a hero” and his and Ms. Walters’ deaths “a terrible tragedy.” It made no mention, however, of Sergeant Walters, the soldier under General Piatt’s command.

Whatever the motive, the killing of the trooper was as sudden as it was shocking, with a tense denouement of drawn weapons in fast-fading daylight, according to police accounts.

Responding to a report of shots fired just after 8 p.m., Trooper Davis parked about 75 feet from the Walters residence, a white double-wide mobile home on a narrow two-lane road with no streetlights. The trooper radioed that shots were being fired, and exited his vehicle to investigate.

Moments later, Trooper Davis was shot, the bullet entering his side, which was unprotected by his bulletproof vest, according to the police. He fell, fatally wounded, into a ditch. Shortly after that, a second, unidentified trooper arrived on the scene, and also heard gunfire. That trooper then saw Sergeant Walters, unarmed, standing in his driveway. The trooper pulled his service weapon and confronted Sergeant Walters, who surrendered.

When other troopers arrived, the body of Ms. Walters — who had been shot multiple times — was found in the driveway. A third victim, Rebecca A. Finkle, was also discovered, shot in her torso, though her injuries were not life-threatening. She is believed to be a friend of Ms. Walters.

Sergeant and Ms. Walters had a 3-year-old child who was unharmed, the police said, though it was unclear where the child was during the episode.