"It's not what you know, it's what you can prove"
As expected the case against Strauss-Kahn was dropped. The easy answer is the privilege answer. People with privilege (read money) tend to get the benefit of the doubt when dealing with the authorities than those without. Of interest is that a good deal of people who would level this charge were happy that OJ Simpson received such treatment (though he made it to court). Still though there is water in that argument. Simply put, if you have a shark of a lawyer you have a better chance at maneuvering the criminal justice system than if you do not. And shark lawyers cost money. Lots of money.
There is however a second issue that is just as if not more important here. The US system of criminal "justice" rests on the concept of reasonable doubt. In a criminal case a jury of 12 "peers" must decide unanimously that a defendant is guilty "beyond reasonable doubt". Not all doubt but reasonable doubt. Furthermore it is the job of the state to furnish this proof. Not the defense. Not the media. Not the organization to which you belong to. The state. A prosecutor must (should) have a reasonable expectation that the charges against an individual will meet this standard. Clearly if the prosecutor thinks that the suspect has a weak defense team or some means of robustly defending himself then the prosecutor is going to be far more careful going about preparing a case than if the suspect is some kid picked up on a street corner drug bust. Strauss-Kahn was a high profile person with a "robust" defense team so even after the show of a perp walk and a stint in Rikers was not going to make him fold like a "regular" jump-out-the-shadows rapist would likely do. The prosecutor knew that if there was ANYTHING in the past of Ms. Diallo, they would use it to destroy her credibility on the stand.
Understand that credibility is what a jury uses to judge whether a witness is credible or not. Why should anybody on a witness stand be believed? Their truthfulness can only be inferred by something else. We use education, diction, body language and the like to determine credibility. We do this all the time. Ask how many people will trust the word of someone caught lying about anything in the past and they will tell you that their trust is lowered by such an event. If that person is caught lying multiple times, then that trust is lowered even more. If that person has been caught lying about the same thing they are trying to convince you about how trustworthy would you find them? Exactly.
This was the problem that the prosecution faced. It is not that it was unlikely that Ms. Diallo was lying about what happened in the Sofitel that day. It was that they had proof that she lied about a number of things including a rape claim. If anything that one lie on her asylum application was the most damaging item that the prosecution had to deal with. Statistically men are less likely to believe in a rape accusation. Men are also far less sympathetic to women who have lied about a rape. There's nothing nefarious about this. It is self interest. As a man being accused of rape is a big deal. If the prosecution had to deal with any men in the jury it would take only one to not believe Ms. Diallo for there to be an acquittal. Add to the rape issue the evidence that Ms. Diallo spoke via telephone to a drug dealer of some sort about the case, allegedly saying that "he's rich" and "I know what I'm doing" you have enough technical reasonable doubt that any prosecutor is going to question the strength of his case, particularly in the face of a high profile defendant.
How would the defense play these two pieces of information? Simple. First they will concede to all the forensic evidence. They will say that a consensual sex act(s) occur ed and that Strauss-Khan is particularly aggressive and that explains the alleged digital bruising to the vagina. They will explain that Strauss-Kahn did in fact comment about his position as head of IMF as a means to take away fear of Ms. Diallo losing her job and the payment that would be coming her way (though that would open him up to solicitation charges but lets run with this). They will say that for whatever reason she was upset about the money (or him having ejaculated in her mouth, who knows) and decided that she either wanted more money (backed up by the recent news of a civil suit) or revenge (also backed up by the civil suit). They will say that Ms. Diallo has, in the past used rape as a means of getting what she wanted (asylum) so it isn't unreasonable to think that she is doing so again. Then they'll trot out all the unsavory people she has been associating with. They would question why this woman did not fight this man off. They will ask where are the bruises. They will ask, what kind of woman would allow a man to do these things and offer no resistance that would mark a naked man. Yes, this would be a "blame the victim" fest at it's ugliest.
Does this mean that I think Strauss-Khan did not commit the crime? No. I think he did. His history, which would have been introduced into court (though I have questions as to it's admissibility )indicates a high likelihood that he did in fact attack Ms. Diallo. But as Alonzo of Training Day fame asked: It's not what you know, it's what you can prove. Prior history may serve as a pointer but it does not prove this case and the burden of proof is on the state not on the defense.
I would have loved to see Ms. Diallo get her day in criminal court and let the jury decide but I completely understand why this went the way it did.