A NEW chief prosecutor, Steve T. Descano, has been elected and will soon take office in Fairfax County, Virginia’s largest jurisdiction. His first order of business should be to open an investigation into the killing of Bijan Ghaisar, the unarmed 25-year-old accountant shot to death two years ago by a pair of U.S. Park Police officers who opened fire without justification.

Mr. Descano ran on the premise that citizens need not “choose between safety and their values,” as he put it. As it happens, safely and values would dovetail neatly in seeking justice for Mr. Ghaisar, who posed no threat to anyone, and who was killed after his vehicle was rear-ended in a minor fender bender.

On Thursday, federal prosecutors announced they would not bring charges against the police officers in the case. They released almost no information gathered by the FBI in the course of a two-year investigation, during which agents supposedly interviewed more than 150 individuals — a bizarre claim given the existence of a clear and complete videotape of the incident. Mr. Ghaisar’s family is pursuing a federal lawsuit against the officers. However, neither the federal abdication nor the family’s lawsuit preclude criminal charges by Virginia against the officers.

The outcome of the federal investigation transmits the unmistakable message that police in the line of duty have virtual carte blanche to shoot and kill people, for any reason or no reason at all. That travesty demands a correction; Mr. Descano could deliver it.

A state prosecution in the Ghaisar case may raise some legal questions. One is whether federal authorities would cooperate with state prosecutors by handing over evidence gathered by the FBI. Until now, virtually no evidence has been disclosed, nor any explanation for the shooting offered by officials who have cited an ongoing federal investigation as their excuse. That excuse is no longer valid.

It is also possible that the police may try to shift the case from state court to federal court, a move for which there appears to be precedent when federal officers are involved. If that happens, they could seek to dismiss charges by asserting immunity from state prosecution under the Constitution’s supremacy clause, under which federal laws take priority over state ones, or force prosecutors to disprove the officers’ assertion they acted in self-defense (as they have claimed in the civil suit).

Mr. Descano’s responsibility would be to prepare for such a defense strategy, not acquiesce to it. The federal government threw up its hands, in effect saying police can get away with murder when it’s committed in the line of duty. The state of Virginia can and should do better.

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