FBI Director Christopher A. Wray in Washington on Oct. 13, 2017. (Chip Somodevilla/Getty Images)

IN A message introducing his agency’s annual report on crime in 2016, FBI Director Christopher A. Wray led with the basics. “In law enforcement we must be accountable to the people we serve,” he wrote. “To be accountable, we must be transparent. We are transparent when we share data and the circumstances surrounding crime rates, and incidents involving law enforcement’s use of force.”

Fine words. If only Mr. Wray and the FBI lived up to them in the case of Bijan Ghaisar, whose unwarranted killing at the hands of U.S. Park Police continues to languish somewhere in the agency’s investigation files.

For 13 months, the bureau has been in charge of investigating the circumstances surrounding the death of Ghaisar, a 25-year-old accountant who died after two Park Police officers shot him repeatedly, at close range, just south of Alexandria near the Potomac River. Ghaisar was unarmed; he had no criminal history; and dashboard-camera video of the shooting shows he posed no threat to the Park Police officers who pursued and shot him after his car was involved in a minor fender-bender on the George Washington Parkway.

For 13 months, the FBI has been silent. For 13 months, not a word of information has emerged to illuminate why Ghaisar was shot, the thinking and conduct of the officers who shot him, or the reasons for the glacial pace of the investigation. The officers, still unidentified, remain on the Park Police payroll, assigned to administrative duty.

Justice delayed is justice denied — and in the case of Ghaisar’s death, the delay is now so prolonged as to constitute a scandal. The Park Police, having turned over the investigation to the FBI, is mum. Neither agency has reached out to Ghaisar’s parents. And a police shooting that looked unjustified from the outset by now takes on the characteristics of a coverup: stonewalling, unaccountability and a code of silence whose effect is to protect uniformed officers from the consequences of their poor judgment.

None of that is to excuse the actions of Ghaisar, who kept driving after his vehicle was rear-ended. Then, when pursued by the Park Police patrol car, he pulled over twice and, when the officers approached him with guns drawn — an unjustified tactic — drove off twice. When he pulled over a third time, then slowly rolled away from the officers who again approached with guns drawn, they opened fire.

How did a small-time collision result in such a sequence of events? Why did the officers draw their guns, in contravention of most police department guidelines? On what basis did they justify pulling their triggers?

Those are the straightforward questions the FBI is charged with answering to satisfy Mr. Wray’s own plain-spoken directives about transparency and accountability. To date, it has failed, and that failure subverts public trust in the nation’s leading law enforcement agency.