The acquittal by Pennsylvania’s top court of Bill Cosby on all the charges on which he’d been cast into prison is a reminder — oh, how we need it — of the primacy of due process in our system of justice. The actor had been convicted of sexually assaulting Andrea Constand. The case took on a political overtone amid the #MeToo against sexual harassment. Did that pressure lead prosecutors to run the warning lights of due process?

These flashed in 2005, when the prosecutor leading the investigation of Ms. Constand’s charges — Bruce Castor — concluded he couldn’t win the case. To salvage something of it, he promised Mr. Cosby that if he cooperated in Ms. Constand’s civil case, Pennsylvania would again never levy criminal charges in the matter. Fair enough. Mr. Cosby forsook his Fifth Amendment right against self-incrimination and testified.

The result was not nothing. Ms. Constand won a settlement of $3.8 million. Years later, though, as sexual assault emerged as a leading national issue, Pennsylvania broke its agreement. There was a good bit of dispute about how serious an agreement it was — and whether it was properly laid before a judge, and the like. When it finally got to the state’s supreme court, though, the justices ruled six to one that the agreement was binding.

“We hold,” they wrote in no uncertain terms, “that, when a prosecutor makes an unconditional promise of nonprosecution, and when the defendant relies upon that guarantee to the detriment of his constitutional right not to testify, the principle of fundamental fairness that undergirds due process of law in our criminal justice system demands that the promise be enforced.”

It’s nice, we don’t mind saying, to hear that from a court. It wouldn’t surprise us were it being flyspecked around the courthouse where, say, Ghislaine Maxwell is due to be tried for her alleged role in Jeffrey Epstein’s crimes. Ms. Maxwell has sought shelter under a nonprosecution agreement struck in Florida between America and Epstein — a pact that allegedly covered his employees. In April, a judge swatted away her plea.

Then again, too, the trial judge in Mr. Cosby’s case also dismissed efforts to hold Pennsylvania to the promise it originally made to the comic. The issues surrounding the nonprosecution agreements in the two cases aren’t completely analogous. Yet it wouldn’t surprise us if Ms. Maxwell’s lawyers are suddenly studying the Cosby case, where the court made an all-too-rarely-remembered point about prosecutors.

“Prosecutors are more than mere participants in our criminal justice system,” the court said. “They are officers of the court, advocates for victims, and administrators of justice. As the Commonwealth’s representatives, prosecutors are duty-bound to pursue ‘equal and impartial justice,’ and ‘to serve the public interest.’ Their obligation is ‘not merely to convict,’ but rather to ‘seek justice within the bounds of the law.’”

No doubt this is an understandably discouraging moment for Ms. Constand and other women who have alleged that they were assaulted by Mr. Cosby. The actor himself has maintained his innocence throughout. He, though, has not been declared innocent. For it is not in the power of our courts to pronounce innocence in criminal cases. The part of the courts is to decide guilty or not guilty. The burden is never on the victim — or the accused. It’s entirely on the state.