Cathy Lanier, chief of the D.C. police, testifies on Capitol Hill in January. (Evan Vucci/AP)

The D.C. police chief has asked federal authorities to review the city’s handling of sexual-assault reports after a human rights group complained that detectives in recent years failed to conduct investigations in many cases and routinely behaved “in a dismissive or insensitive manner” toward alleged victims.

New York-based Human Rights Watch said that after researching cases dating as far back as 2006, it intended to publish a study criticizing the way D.C. police deal with reports of sexual assault involving adults later this month. The group summarized its study in a May 30 letter to Police Chief Cathy L. Lanier, who disputed the findings and asked the Justice Department to conduct a review “as an impartial third party.” She sent her request to the Justice Department’s civil rights division.

A Justice Department spokesman, Mitchell Rivard, declined to comment on what action, if any, the federal agency might take.

Late Thursday evening, Lanier met with the study’s author, Human Rights Watch lawyer Sara Darehshori. Lanier agreed to make additional departmental files covering sex assault cases available to Darehshori; Darehshori said her group will publish its report after seeing the files.

“We asked for a delay in the report until they see that data, and they agreed to that,” Lanier said in an interview. “Any future reforms that they are seeking to have done have to be based on accurate data.”

“I want the report to be as fair and as accurate as possible,” Darehshori said in an interview. “I’m willing to look into their files and to turn over every stone.”

In her May letter to Lanier, Darehshori says her research indicated that the number of sexual assaults reported at MedStar Washington Hospital Center in recent years was far higher than the number investigated by police, suggesting that detectives were quick to dismiss many reports as untrue. Interviews with alleged victims, hospital workers and others supported that conclusion, she said.

“Our research indicates that a significant number of sexual-assault cases are not being documented” by police, Darehshori said in her letter to Lanier.

Darehshori also cited the “re­victimization” of women, telling Lanier that “detectives regularly treat victims in a dismissive or insensitive manner, adding to their trauma and undermining the possibility that their perpetrator will be brought to justice.”

The behavior included “questioning survivors’ credibility; actively discouraging victims from reporting or providing forensic evidence; threatening victims with prosecution if they are found to be lying; asking victim-blaming or inappropriate questions; telling victims that their stories are not serious enough to investigate; and failing to keep victims informed of progress on their cases,” Darehshori wrote.

In a June 8 written response to Human Rights Watch, Lanier said she agreed with many of the group’s recommendations for improving the way sexual-assault cases are handled.

“We have identified a number of potential fundamental and disturbing flaws in your investigation,” Lanier told Darehshori. “If the letter in any way resembles the full investigation,” Lanier wrote, “we believe the matter needs further and more thorough investigation to support and/or substantiate the allegations that you have made.”

Lanier also criticized Human Rights Watch for not giving her the entire report before asking for a response. Darehshori said in an interview that the group, as a matter of policy, does not provide the subject of a report with an advance copy of the document.

Without seeing the full report, Lanier said, she could not tell whether the problems cited by Human Rights Watch predate changes that she ordered in sexual-assault investigations in 2008. Those changes included better training, a more extensive case-review process by supervisors, stricter selection criteria for new sexual-assault detectives and increased cooperation between police and hospitals, Lanier said.

“These reforms culminated in final revisions, published in August 2011, to policies and procedures for [the police department’s] Sex Assault Unit, which handles these difficult investigations,” she said in the letter asking Thomas E. Perez, the assistant attorney for civil rights.

“I believe that the Sexual Assault Unit is providing dedicated service to victims in need and has embraced these reforms that have strengthened their efforts and collaboration with the community,” the chief wrote.