THE DISGRACE of the foot-dragging, stonewalling, shoulder-shrugging two-year FBI investigation into the unwarranted killing of an unarmed man near the District by U.S. Park Police officers in November 2017 has now reached a contemptible travesty of a climax: a decision Wednesday by federal prosecutors to close the case with no charges.

The victim, Bijan Ghaisar, a charismatic, football-loving 25-year-old accountant beloved by his many friends and family, was shot repeatedly in the head by a pair of officers after his vehicle was rear-ended in a minor fender bender in the Northern Virginia suburbs. As is obvious from dash-cam video footage of the incident, the officers brandished their weapons for no good reason and opened fire even though Ghaisar posed no threat to them or anyone else.

The killing amounted to an execution by officers sworn to uphold the law, who appeared exasperated that Ghaisar, perhaps terrified that the officers had approached him with guns drawn, drove off twice after being stopped before the final, fatal encounter. To be clear: Exasperation does not give police a license to kill. Or at least — we would have thought until this decision that it does not.

Jessie K. Liu, the U.S. attorney for the District of Columbia, and Justice Department officials say they have concluded that evidence is lacking to prove the officers “willfully” took Ghaisar’s life. To grasp how that offends any notion of justice, one need only watch the video. To see the footage and then assert the officers did not “willfully” shoot Ghaisar is to proclaim that grass is purple.

Ms. Liu’s office, in announcing its decision, said that “evidence that an officer acted out of fear, mistake, panic, misperception, negligence or even poor judgment cannot establish the high level of intent required” under the law. A “willful” police shooting, the office said, must meet the Supreme Court’s standard: an act impelled by “a bad purpose to disregard the law.”

If repeatedly shooting an unarmed man — a man who imperiled no one — does not amount to “a bad purpose to disregard the law,” then those words are devoid of meaning. And no police officer will ever be charged, no matter how egregious the case.

The baffling ending to the criminal case is of a piece with the unjustified duration of the investigation, in the course of which the FBI arrogantly ignored requests for meetings and substantive updates from three senators, a member of the House and the Ghaisar family and lawyer. It is in line with the refusal of Park Police officials to furnish the public with even the most basic information about the incident, including, for more than a year, the names of the two officers: Alejandro Amaya and Lucas Vinyard. And it is in keeping with the inhumane actions of police who refused to allow Ghaisar’s family to touch him when he lay in a coma for 10 days before dying and referred to him as “the perp” (as in perpetrator).

The common thread is arrogance and unaccountability. The final evidence of that posture is prosecutors’ refusal to put the evidence before a grand jury.

The Ghaisar family has filed a civil suit against the police. It is their final recourse and last hope to secure a modest measure of justice in a case that has enshrined injustice, and in doing so disgraced the nation.

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