A stuffed teddy bear hangs on a street sign during a vigil for Terrence Sterling. (Ricky Carioti/The Washington Post)

AS SEASONED prosecutors know, juries are generally loath to convict police officers, including in fatal shootings or negligent deaths, especially if there is a remotely plausible case that the officer acted in self-defense. To secure a guilty verdict, a jury would have to find, beyond a reasonable doubt, that an officer had no cause to fear for his or her life and had intentionally used excessive force — a tall order.

So it is perhaps unsurprising that the U.S. Attorney’s Office for the District of Columbia declined to seek criminal charges against a District police officer, Brian Trainer, who fatally shot an unarmed motorcyclist in September. The motorcyclist, Terrence Sterling, 31, had allegedly led officers on a pre-dawn, high-speed chase in Northwest Washington. His blood alcohol level was twice the legal limit, and tests indicated he’d been smoking marijuana. When a police car finally pulled in front of Sterling, in an attempt to apprehend him, he revved his bike and bumped it into the car’s door as Mr. Trainer tried to exit the vehicle, denting it. Mr. Trainer then fired two shots through the patrol car’s open window, killing Sterling.

As is often the case, the facts are less than clear-cut. Two witnesses who saw the shooting said Sterling seemed intent on evading the police, not hurting them. They said the officer issued no warning before opening fire. Whether Mr. Trainer had a reasonable fear that his life was in jeopardy, and really acted in self-defense, would have been a major point of contention at trial, had there been one. And remember: Juries are generally reluctant to convict police officers who can make a plausible case.

Mr. Trainer, who has been an officer for five years, has been asked to resign by the police force, which is conducting an internal investigation of his actions up to and including the shooting. He is also the subject of a $50 million wrongful-death suit brought by Sterling’s family. He may still face consequences, in other words.

Nonetheless, there are legitimate questions about whether the police have been subject to real accountability in Sterling’s death, especially given that no District police officer has ever been the subject of criminal charges for a fatal shooting in the line of duty. The fact that Mr. Trainer did not activate his body-worn camera until at least a minute after the shooting only deepens concerns about this incident. And it’s troubling that it took the U.S. Attorney’s Office 11 months to reach its decision not to indict.

A wide-ranging independent report last year on police reforms concluded that intentional shootings by District police officers had decreased sharply since the turn of the century, with officer-involved fatal shootings in the relatively low range of three to eight annually since 2009. That’s encouraging, but it does not justify even one unnecessary — and possibly unwarranted — death.