Bijan C. Ghaisar, 25, of McLean, Va. (Family photo)

IN THE taxonomy of Washington-area law enforcement agencies, the U.S. Park Police — understaffed, underrecognized and under the radar — rarely finds itself the subject of intense scrutiny. Nor are its uniformed officers, who patrol monuments as well as the George Washington Memorial and Baltimore-Washington parkways and are called on to control crowds and respond to vehicle accidents, often in the business of discharging their weapons.

Despite that, the Park Police, a part of the National Park Service, is under the microscope for a barely explained incident Nov. 17 in which at least one of its officers opened fire on an apparently unarmed motorist after an alleged hit-and-run accident on the G.W. Parkway. The motorist, who never regained consciousness, died on Monday.

It is anyone’s guess why this incident ended in death, because everyone even tangentially involved in it has clammed up — the Park Police, whose officer or officers shot the man at least twice in the head; the Fairfax County police, whose own officers, tailing the Park Police vehicle, apparently recorded the shooting with their dashboard camera; and the FBI, to which the Park Police transferred the investigation a few days after the incident.

It is unacceptable that the authorities have draped a veil of secrecy over the death of the driver, Bijan C. Ghaisar of McLean, a 25-year-old accountant born and raised in Virginia who had no reported history of violence or serious criminality. It is outrageous that they have explained nothing of the alleged hit-and-run that triggered the incident — the stuff of quotidian police blotters. And it is intolerable that they have refused to say for what reason the officer or officers opened fire, and that they have not identified the officers. A man is dead, but why?

Law enforcement agencies, no less than other agencies of government, owe a debt of transparency to the taxpayers who fund them. In this incident, by their silence, the relevant police and investigators do nothing to enhance their investigation. But they do plenty to cultivate public suspicions that something is being hidden — something embarrassing; something unwarranted; something unconscionable. In the court of public opinion, there is little more damning than the muzzle of official silence that descends after the shooting of an unarmed man.

Rep. Don Beyer, the Northern Virginia Democrat whose district includes the Fort Hunt area of Fairfax County where Mr. Ghaisar was shot, had it right when he said that the shooting “has been shrouded in an unacceptable level of opacity. . . . The public,” he added, “particularly his family and friends, deserve to know what happened here.”

For starters, the public is entitled to see the police dashboard-camera footage of the incident at the earliest possible date. The public also deserves a detailed explanation of what happened after the alleged hit-and-run in Alexandria, in the course of an 11-minute southbound pursuit, and what prompted the bloody ending in Fort Hunt. Secrecy about such events is standard procedure in police states; it doesn’t wash here.