I’ve been to a lot of dinner parties lately where the question du jour is whether Nafissatou Diallo should have been “given her day in court” so she could “fully air” her charges against Dominique Strauss-Kahn; and, while we’re on the topic, whether Manhattan District Attorney Cyrus Vance Jr. compromised his political career with the motion to dismiss. It’s slow around Labor Day, so I understand the hunger to have that case go on forever; it would have been a mega-spectacle, and I, too, would have loved seeing the blood vessels in Nancy Grace’s temples balloon and throb.

Carnival possibilities notwithstanding, however, it’s important to remember that criminal cases fall apart all the time. Through one prism, this was just one of them—such is life. At the same time, as Katha Pollitt noted recently in a post on The Nation’s website, the onus on a victim asserting rape is very, very great. It seems there’s always “something” in her past that can and will be used against her. In addition, the way l’Affaire DSK played with hot-button political figurations—money, race, ethnicity, immigration—made its end especially excruciating. Like a piñata that has spewed its contents after much bashing, a ghostly ruin of pluralized images were left to us: poor hotel workers, haughty Frenchmen, lying black women, callous prosecutors, Muslim mothers, high-priced lawyers, insidious unnamed sources, guys who smile like cats that swallowed the canary and traumatized rape victims everywhere.

It’s important to understand why this case fell apart, to distinguish some of its particular features from the more general challenges in prosecuting rape. First, rape cases are notoriously difficult to prove, because the crime is so often one-on-one, or “he said/she said.” In the past, the mere lack of other witnesses was considered legal reason for letting rape go unprosecuted. This is no longer true—and despite confusing media assertions to the contrary, Diallo’s case was not dismissed on those grounds.

Second, despite our best aphorisms that “even” prostitutes and pathological liars can be raped, it remains true that the credibility of rape victims is too frequently doubted for specious reasons having to do with their sexual history. Media accounts suggested that Diallo’s suit was dismissed because of her “questionable past,” but that wasn’t what weakened the case most. It was that she lied to prosecutors again and again and again. The fact that she falsely claimed* to have been gang-raped in Guinea probably wasn’t enough to doom the case—she might still have presented herself quite sympathetically as a desperate refugee fleeing a war zone—but there were other things undermining her credibility. Diallo repeatedly confused or misrepresented crucial sequences of events to the grand jury, to police and to prosecutors. Not only did the police investigation turn up a jumble of discrepancies in her story; her own attorney permitted her, even advised her, to talk and talk and talk to all manner of tabloid media hounds. That rather unusual—I would say reckless—decision captured yet more discrepancies for the record and diminished her reliability further.

Third, where an accuser’s story becomes subject to documentable weaknesses on this great a scale, it’s the prosecutor’s duty to move for dismissal. What seems to be overlooked in calls to give Diallo “her day in court” is that our criminal justice system pursues cases in the interest of public order, not on behalf of an individual complainant. That’s why criminal cases are titled “The People” of a jurisdiction versus an alleged criminal actor. (A civil—or more “private interest”—claim, on the other hand, would allow “Ms. Diallo as an individual” to bring a case against “Mr. Strauss-Kahn as an individual,” and, given the lighter burden of proof in civil cases, would offer a better chance of winning such a suit.) Vance does not represent either “the police,” as so many seem to think, or Diallo, but rather the broad justice interests of the entire state; it’s the reason he was required to reveal the flaws in her story when the investigation uncovered them. If it’s exculpatory, the defendant has a right to know.

The responsibility of prosecutors to dismiss a weakened case is designed to be a filter of sorts. Not only would it be a waste of public resources to take questionable cases to trial; it would fundamentally challenge the very notions of presumed innocence and reasonable doubt. The prosecutor cannot—as a matter of absolute professional ethics—proceed to trial with a claim where the prime witness repeatedly changes or lies about relevant, substantive elements of the story. This is not a matter of discretion: prosecutors are forbidden from presenting a case to a jury when they do not believe they can win, as judged by the standard of “beyond a reasonable doubt.”

That said, the perceptions of prosecutors in determining who is a credible accuser are inflected by the same biases and assumptions that afflict the culture at large. When it comes to rape cases, data have shown that men are more often believed than women, and whites more than blacks, and fine suits more than sweatpants. Bad prosecutors make bad decisions about witness credibility all the time—and therein lie the grounds for our political advocacy, the reason to keep pressing for more educated participants at every level of the system, from police to prosecutors to judges.

We have plenty of reasons to be worried about the social divides that play out daily in our judicial system. But if there is bias at work in Vance’s handling of his office, this case isn’t the best proof. The wrenching demographics of misogynistic insult, assault and murder cannot alone determine the result of a given “case or controversy” (as our Constitution puts it). Putting them ahead of actual proof to seek vengeance against a “smugly smiling” icon of the banking industry is not so very different from carelessly assuming that a “scowling” black youth “probably” did it because he was wearing a hoodie. We cannot—should not—all be Nancy Grace.

*The original version of this column contained an inaccurate detail regarding Nafissatou Diallo’s asylum application. Ms. Diallo did not lie on her application about being gang-raped in Guinea. Rather, she falsely claimed to prosecutors both that she had been gang-raped and that she had reported the fabricated incident on her application for asylum.