Aug. 22, 2011 -- New York prosecutors today asked a judge to dismiss sexual assault charges against former International Monetary Fund chief Dominique Strauss-Kahn, citing questions about his accuser's truthfulness.

Strauss-Kahn had been accused of sexually assaulting Sofitel Hotel maid Nafissatou Diallo in May.

In a 25-page motion filed with Judge Michael Obus, prosecutors said "evidence gathered in our post indictment investigation severely undermined her reliability as a witness in this case."

During the investigation into the incident, prosecutors say, Diallo presented three different versions of the alleged assault and lied under oath. Her credibility "cannot withstand the most basic evaluation," prosecutors said in the motion.

"If we do not believe her beyond a reasonable doubt, we cannot ask a jury to do so," Assistant District Attorney Joan Illuzzi-Orbon said.

Obus is not expected to rule on the dismissal request until Tuesday, when Strauss-Kahn is scheduled to appear in court, possibly for the last time related to these charges.

Her attorney says Diallo is "devastated" by the decision to abandon the criminal case.

Kenneth Thompson said he still believes there is sufficient physical evidence to overcome any doubts prosecutors have about the hotel maid's credibility.

Thompson told ABC News that today's meeting involving three prosecutors from the office of Manhattan District Attorney Cy Vance, Thompson and Diallo "was hostile."

"Joan Illuzzi [an assistant district attorney] basically told Ms. Diallo that they were dismissing the case, claiming because she lied to them," Thompson said. "They totally disrespected Ms. Diallo by walking out on her while she was trying to ask them a question."

The district attorney's office by practice does not comment on meetings between lawyers.

Strauss-Kahn had long maintained he was innocent of the charges.

"We have maintained from the beginning of this case that our client is innocent," Strauss-Kahn's lawyers, William W. Taylor and Benjamin Brafman, said in a statement. "We also maintained that there were many reasons to believe that Mr. Strauss-Kahn's accuser was not credible. Mr. Strauss-Kahn and his family are grateful that the District Attorney's office took our concerns seriously and concluded on its own that this case cannot proceed further. We look forward to attending the hearing on Tuesday."

In what may have been a last-ditch attempt to change the anticipated outcome of the crumbling case, lawyers for Diallo had earlier filed a motion to disqualify Vance from the case.

"The Manhattan District Attorney has denied the right of a woman to get justice in a rape case. He has not only turned his back on this innocent victim but he has also turned his back on the forensic, medical and other physical evidence in this case," Thompson said in a statement this afternoon.

In the filing to disqualify Vance, Thompson said Vance "has sabotaged Defendant Strauss-Kahn's prosecution."

He said Vance's handling of the case "has been inadequate and troubling."

Thompson accused Vance's office of treating his client "abusively." He said the office failed to refute a New York Post article that called Diallo a hooker.

Thompson also claimed the DA's office was predisposed to dismissing a case it once called "strong." He says an assistant district attorney told Diallo's counsel, "No one with half a brain would ever put her on the stand."

Terry O'Neill, president of the National Organization for Women, said, "It's a very serious, bad message to send to other victims," adding that rape is already an underreported crime.

Prosecutors came to doubt the case, which once appeared strong, because of what they call "substantial credibility issues" related to Diallo's background and conduct.

Questions arose surrounding what happened immediately after the alleged attack and led the Manhattan District Attorney's office to consider whether to drop the charges amid concerns about Diallo's credibility.

Diallo said she was in the hall when Strauss-Kahn left the suite, but hotel records show she briefly went into another room, and then re-entered Strauss-Kahn's suite.

Diallo has also admitted to lying on her tax returns and lying about the details of a rape in her home country of Guinea that helped her to achieve asylum in the United States. But she says that it is irrelevant to what she says happened in Strauss-Kahn's hotel suite.

"I have made mistakes," Diallo conceded to ABC News in July. "But this man tried to rape me."

Strauss-Kahn has denied all charges. His attorneys have suggested the encounter in the Sofitel Hotel suite May 14 was consensual. His attorneys have portrayed Diallo as a woman out for money.

If charges against Strauss-Kahn are dismissed, a dramatic prosecution would end without answering the question of what really happened between one of the world's most powerful men and an immigrant maid inside the hotel suite.

Meanwhile, Diallo's civil lawsuit will continue, even though the criminal case against Strauss-Kahn is ending.

"He has already been served," Diallo's attorney, Douglas Wigdor, said. "He needs to defend."

Marcellus McRae, a trial lawyer in the Los Angeles office of Gibson Dunn, who is not involved in the case, said Diallo might lack the resources to engage in a contentious battle.

"And she still has myriad credibility problems," McRae said.