Editor's note: Jeffrey Toobin is a senior legal analyst for CNN and a staff writer at The New Yorker magazine, where he covers legal affairs.
(CNN) -- The sexual assault case against Dominique Strauss-Kahn is now over. The judge has granted the prosecutors' motion to dismiss the case against the former head of the International Monetary Fund. But for all the complex legal machinations, one simple question remains unanswered: What happened between Strauss-Kahn and Nafissatou Diallo, the housekeeper at the Sofitel in New York, on May 14?
The answer -- or nonanswer -- explains something about our legal system. Cyrus Vance Jr., the Manhattan district attorney, moved to dismiss the case against Stauss-Kahn because his staff came to believe that Diallo could not be trusted as a witness.
"The nature and number of the complainant's falsehoods leave us unable to credit her version of events beyond a reasonable doubt, whatever the truth may be about the encounter between the complainant and the defendant," the prosecutors wrote in a 25-page brief filed Monday. "If we do not believe her beyond a reasonable doubt, we cannot ask a jury to do so."
Notice the key phrase, "whatever the truth may be." Like any prosecutor, Vance is concerned above all with what he can prove, not "the truth." As the prosecutors detailed in their brief, Diallo's credibility problems were extraordinary. In their account, she lied about the chronology of events with Strauss-Kahn, about her background, about her finances, about her associates and much else besides.
The prosecutors do not say that she lied about what happened in the hotel room with Strauss-Kahn. Their judgment is narrower; because of her lies about other subjects, a jury would never believe her account of the events in question.
If Diallo had taken the stand at a trial, she would have been subject to ferocious cross-examination by Benjamin Brafman, who is one of the best lawyers in the business. But what would Brafman have been trying to do? He would have tried to persuade the jury that Diallo was not worthy of belief, and based on the prosecutors' submission, he would have had a great deal of ammunition to make that case.
But Brafman's task, by design, would have been destructive, not constructive. His only duty would have been to tear down the story that Diallo told, not to build a credible one of his own. That's what the burden of proof means. Prosecutors have to prove their case; the defense need only poke holes, not present an alternative.
The prosecutors' account of the actions of Strauss-Kahn are similarly narrow. The picture they paint of him is an ugly one. Within minutes of Diallo's arrival in his hotel room, she was spitting out his semen in the hotel hallway. But the prosecutors say that, at this point, they cannot prove that Strauss-Kahn assaulted Diallo. At a minimum, it seems, Strauss-Kahn behaved like a cad and a creep, but that is a moral, not legal, judgment.
In sum, then, none of the parties in the case are principally concerned with determining the "truth" of what went on in that room. (Journalism, in its imperfect way, is concerned with determining truth.) The prosecution and defense are concerned only with what they can prove, or disprove, in a courtroom. That's not a criticism, just a reflection of how our system works. So what happened in that hotel room? Chances are, we'll never know.
The opinions expressed in this commentary are solely those of Jeffrey Toobin.