DURHAM, N.C. — The district attorney dropped rape charges Friday against the three Duke University lacrosse players after the stripper who accused them changed her story again. But the men still face kidnapping and sex charges that could bring more than 30 years in prison.

A lawyer for one of the athletes bitterly demanded that District Attorney Mike Nifong drop the remaining counts, accusing him of offering shifting theories of the crime in an attempt to win the case at any cost.

“It’s now the shifting sands again, the shifting factual theory,” defense attorney Joseph Cheshire said. He added: “It is the ethical duty of a district attorney not to win a case, not to prosecute all cases, but to see that justice is done.”

In dropping the rape charges, Nifong filed court papers that said the accuser [Crystal Gayle Mangum] told an investigator Thursday that she is no longer certain whether she was penetrated vaginally with the men’s penises, as she had claimed earlier. Nifong previously said he would rely on the woman’s account because of a lack of DNA evidence against the players.

Lacking any “scientific or other evidence independent of the victim’s testimony” to corroborate that aspect of the case, the district attorney said in court papers, “the state is unable to meet its burden of proof with respect to this offense.”

Nifong did not immediately return calls for comment, and a sign posted on his office door read, “No media, please!”

In recent months, Nifong has been vilified by some lawyers and members of the community for pressing ahead with what appeared to many to be a remarkably weak case.

“He has said to you his case rises and falls on the statements of the accuser,” Cheshire said of the district attorney. “He gets yet again a different story from her, which disputes and goes against the other stories she has told.”

The accuser, a 28-year-old student at North Carolina Central University, has said three men raped her — vaginally, anally and orally — while holding her against her will in a bathroom at a March 13 Duke lacrosse team party where she was hired to perform as a stripper.

The indicted players — Dave Evans, Collin Finnerty and Reade Seligmann — all say they are innocent. Their attorneys have consistently said no sex occurred at the party.

The men are still charged with kidnapping, for allegedly holding the woman against her will, and sexual offense. Under state law, a rape charge requires vaginal intercourse, while sexual offense covers any sexual act. In dropping the rape charges, Nifong did not specify what sex acts prosecutors now believe occurred.

A defendant’s prior criminal record affects the length of a prison sentence in North Carolina. In the case of the three indicted players, Cheshire said rape and sexual offense carry the same possible sentence of up to 24 years in prison, while kidnapping is punishable by up to seven years.

“There’s not a spider web of evidence supporting the allegations of Mr. Nifong,” said Wade Smith, one of the players’ attorneys. “We’ve waited and there hasn’t been anything. … We have this bare assertion and nothing else.”

The defense has complained that the stripper has given authorities at least a dozen different versions of her story. Among other things, she has given conflicting accounts of the number of attackers — anywhere from three to 20 — and the ways in which she was supposedly assaulted. At least one time after the party, she told police she had not been assaulted.

Last week, it was learned that DNA testing arranged by the prosecution at a private laboratory found genetic material from several men on the stripper’s underwear and body, but that none of it came from the players.

“The reality is, what else could the DA do?” said Stan Goldman, who teaches criminal law at Loyola Law School in Los Angeles. “Once the DNA evidence came out last week, I can’t imagine how they could sustain a rape charge.”

But Wendy Murphy, a former prosecutor who teaches at the New England School of Law, said the decision could actually help Nifong by keeping any discussion about the results of the DNA testing away from the jury.

“It may be that this is a strategic move to insulate the trial itself from a sideshow that certainly would have overwhelmed all the other evidence,” Murphy said. “A sideshow about her sex life.”

Even so, the changing story hurts Nifong’s case on the other charges, Goldman said. “It strikes me that a case based on this particular complaining witnesses’ credibility appears to be in jeopardy,” he said.

Evans graduated in May, the day before he was indicted. Sophomores Finnerty and Seligmann were suspended following their April indictments.

“I am greatly relieved for the students and their families that the most serious of the charges has been dropped,” said Duke President Richard Brodhead in a statement. “Given the certainty with which the district attorney made his many public statements regarding the rape allegation, his decision today to drop that charge must call into question the validity of the remaining charges.”