The 32-year-old woman was walking through a midtown alley last January when a man pressed a gun to her shoulder and told her, "Don't scream."

At the hospital, where she was treated for vaginal bleeding, the woman recounted being raped at gunpoint, in a vehicle with black leather seats. When it was over, her attacker told her to walk away slowly and not look back.

The police detective's report reflects the tone of his questioning in the hospital room: Why had she waited two hours to call police? Why didn't she flag down a squad car? Where was she coming from before she was assaulted? Who was she with? Frustrated, the woman retracted her statement and signed a new one saying that nothing had happened.

No longer a rape, the incident was now classified as "unfounded," police parlance for saying the victim was lying or they do not believe a crime occurred.

It's the type of change that happens dozens of times each year, and more often in Baltimore than any place else.

The Baltimore Police Department has for the past four years recorded the highest percentage of rape cases that officers conclude are false or baseless of any city in the country, according to The Baltimore Sun's review of FBI data.

More than 30 percent of the cases investigated by detectives each year are deemed unfounded, five times the national average. Only Louisville and Pittsburgh have reported similar numbers in the recent past, and the number of unfounded rape cases in those cities dropped after police implemented new classification procedures.

The problem in Baltimore may go deeper.

In 4 of 10 emergency calls to police involving allegations of rape, officers conclude that there is no need for a further review, so the case never makes it to detectives — a proportion that experts say is disturbingly high.

The increase in unfounded cases comes as the number of rapes reported by Baltimore police has plunged —from 684 in 1995 to 158 last year, a decline of nearly 80 percent. Nationally, FBI reports indicate that rapes have fallen 8 percent over the same period.

Advocates who work with rape victims and experts who have reviewed police figures in other cities say they are concerned about Baltimore's statistics. They worry that investigative tactics used by police might distort the scope of the problem and discourage victims from coming forward.

They say Baltimore police have expressed a commitment to working with medical providers and victims groups, and they praise the efforts of many detectives. Still, women continue to report that they are interrogated by detectives, sometimes questioned in the emergency room or threatened with being hooked up to lie detectors.

Overall, say those who have reviewed the findings, the numbers just don't add up.

"There's nothing that we see in our work that makes a [more than] two-thirds drop in the number of sexual assaults and rapes in Baltimore make any sense, on any planet," said Rosalyn Branson, executive director of Turn Around, a Towson-based group for victims of sexual assault and domestic violence.

Baltimore's "excessively high unfounded rate with such a small number of rapes reported in the first place" should merit a look from the FBI, said Carol E. Tracy, who works with a nonprofit that has been reviewing rape reports for Philadelphia police for a decade. In that city, the department had been systematically miscounting sexual crimes.

Current and former sex offense detectives in Baltimore defended their investigations. Part of their mission, they say, involves rooting out illegitimate complaints that in the past would result in wasted effort and false arrests.

Many reports of rape are made for "ill gain, in order to gain assistance or cover up not coming home," said one of the commanders of the unit, Lt. Thomas Uzarowski, in a March interview.

"The bottom line is, the case is only unfounded when the investigative facts prove the crime did not occur," said Uzarowski, who retired from the department this month. "It's not an opinion. It's not anything other than where the facts fall."

While Police Commissioner Frederick H. Bealefeld III and other top officials declined requests for interviews, Mayor Stephanie Rawlings-Blake ordered an audit of police procedures and statistics last week after The Baltimore Sun contacted her aides about these findings.