Manhattan District Attorney Cyrus Vance's request for dismissal of all sexual assault charges against former IMF chief Dominique Strauss-Kahn is a stunning reversal by the prosecutors office. Rarely is a "recommendation for dismissal" motion made.

So why would the D.A. change course in such a high-profile case? The reason is simple: they have lost faith in the truthfulness of their own complaining witness.

In a 25-page document filed with the court, the prosecution alleges that the "victim" Nafissatou Diallo attested to three different versions of the event.

Even more stunning they allege she "made false statements under oath in testimony before the grand jury."

The District Attorney's office also states that Diallo made up a story about being gang raped in her country and used that as a reason to gain asylum in the United States.

Add to this the fact that she failed to disclose a stream of income deposited into her checking account of $60,000. In itself, that is not so bad except that the money came from individuals in four different states and the defendant admits she funneled the money elsewhere and that only a percentage of it stayed in her account.

So what does this have to do with the rape charge against Dominique Strauss-Kahn?

The issue of force and lack of consent rest entirely on the believability of this witness. Yes, there is forensic and physical evidence; yes there is a prompt outcry from the alleged victim but the key issue is whether the sex was committed by forcible compulsion. For that there is no corroboration -- only a "he said, she said." The defendant in this case thus gets the benefit of the doubt.

The burden on the prosecution in any criminal case is great -- they must prove a crime was committed beyond a reasonable doubt.

Bottom line: If the District Attorney's team is not convinced of the truthfulness of their own complaining witness they cannot convince twelve jurors to convict based on that witness' testimony.

Judge Jeanine Pirro is the host of "Justice with Judge Jeanine" which airs Saturday evenings at 9 p.m. ET on Fox News Channel. She is also the host of a daytime courtshow "Judge Pirro." She is a former County Court Judge and District Attorney of Westchester County, New York .