MHAI SCOTT, an immigrant from the Philippines, was a tiny woman, barely over five feet tall and not much more than 100 pounds. Yet when a pair of Loudoun County sheriff’s deputies encountered her last Wednesday, behaving erratically and wielding a long-bladed knife and scissors at a Costco in Sterling where she worked, they evidently considered her menacing. In the ensuing confrontation, which may have lasted just a few seconds, she was shot to death by one of the deputies.

Was her death necessary?

The county sheriff, Michael L. Chapman, seems to think his deputies had no choice but to shoot Ms. Scott, 38, who was working as a pizza server at the time of her death. Based on what he acknowledges is preliminary information, he says the officers acted according to procedure, in justified self-defense, when Ms. Scott came at them with the knife.

That may be the case, and so far there is no hard information to cast doubt on the official version of events. The two deputies, who are now on paid administrative leave pending the investigation’s outcome, each had at least several years of experience. They were up to date on training and techniques, according to the sheriff’s office.

Nonetheless, the sheriff’s statement seems not just preliminary but premature. By his own account, something did go badly wrong. Specifically, he said, when one officer attempted to use a Taser to subdue Ms. Scott, it “didn’t work.”

That’s curious and concerning. It’s also unclear. Did the officer who fired the Taser miss Ms. Scott? Did the device malfunction? Was Ms. Scott somehow, unlikely as it seems, impervious to the electroshock?

In fact, Tasers are relatively simple to use and generally highly effective, delivering a potent jolt from a range of up to 20 feet that almost always incapacitates the subject. The sheriff’s office needs to find out why the Taser failed — and explain why Option B was to fire a volley of bullets at Ms. Scott in a shopping aisle.

Fortunately for investigators, there were apparently no shortage of witnesses in Costco to the incident, and the store’s own internal security video may also have recorded it. Given the extraordinary circumstances — a fatal shooting at mid-afternoon in a popular store in plain view of shoppers — the authorities would be well advised to release whatever footage of the incident exists as soon as possible. Failing to do so will only invite further questions, and suspicions, about the prudence of the deputies’ actions and the circumstances of Ms. Scott’s death.

The ambassador from the Philippines, Jose Cuisia, raised the possibility that the deputies used excessive force. He asked that authorities conduct an aggressive and impartial investigation. Ms. Scott certainly deserves that, and so do residents of Loudoun County.