A human rights group that accused D.C. police of failing to investigate scores of sexual assault complaints made faulty assumptions and used incomplete data, according to an independent report set for release Thursday.

The confidential report, produced for the D.C. Council by the law firm Crowell & Moring, concluded that police have accounted for all but five of 170 reports that Human Rights Watch had alleged were missing or had been filed in a way that ensured they would never be properly investigated.

The report, a copy of which was obtained by The Washington Post, credits the rights group with casting a “spotlight on an aspect of law enforcement that is not often discussed,” because of the intimate nature of the crimes. It calls the Human Rights Watch analysis a catalyst for positive change.

Investigators — led by two former prosecutors — urged D.C. police to improve the way they communicate with victims and notes that mistakes were made in some of 1,500 cases handled in the period studied by the rights group, October 2008 through September 2011 .

Detectives falsely classified eight cases, police told Crowell & Moring, and closed some cases prematurely. But the independent review, sought by council member Tommy Wells (D-Ward 6), who chairs the public safety committee, largely backs the long-stated position of Police Chief Cathy L. Lanier.

The law firm criticized the rights group for filling its report with 100 separate stories and quotes from eight women, scattering their statements throughout the 196 pages, creating the impression that they “represent a majority or large percentage of ­cases.”

Wells’s committee will meet Thursday for a roundtable discussion with representatives of the law firm, who will present their findings. There will be no public testimony, although police officials and the author of the rights watch report, Sara Darehshori, will be present. Council members will decide later whether legislation is needed to implement any reforms.

Wells said that the allegations were inflammatory and that it was ”extremely important to bring in a third party that has unquestioned ability to sort this out on behalf of the city. . . . I feel assured of the police department’s ability to respond to sexual assaults.”

Lanier said in a statement that the review has “reinforced our conclusions” that the investigation reflected “a deliberate bias against the department.” She added, “Over the past five years, MPD and the District’s entire criminal justice and victims’ services system have been working together to improve the response to our investigation of sexual assaults.”

Human Rights Watch urged the council to press for external oversight to ensure ­changes are made. Darehshori said there are outstanding issues, and she isn’t satisfied that all sexual assault reports have been accounted for. “It doesn’t seem to vindicate the police department,” she said.

Human Rights Watch released its report in January. Titled “Capitol Offense,” it portrayed D.C. police as callously disregarding rape victims and what the group alleged was a coordinated effort to play down the crimes. It raised questions of confidence for the police, which Lanier said could undermine her efforts to persuade women to talk to officers in what is considered one of most underreported crimes.

Among the more serious allegations leveled by Human Rights Watch was that it found 170 sexual assault cases in which women sought medical treatment and said they requested police, but no police report or other documentation could be found. That represented more than a third of the 480 cases reviewed by the group.

The rights group, without access to victims’ names, tried to match the hospital reports to public police reports, which are supposed to be filed within 24 hours of a complaint. But Crowell & Moring agreed with police that this methodology was flawed.

A victim can go to the police before going to the hospital, and she has up to 96 hours to seek what is called SANE exam, short for sexual assault nurse examiner. That means the rights group could have missed police reports taken outside the 24-hour window it used.

The report said police retraced the rights group’s steps, but using victims’ names. Of the 170 reports Human Rights Watch said were missing, Crowell & Moring said it concluded that in 19 cases, women sought medical attention in the District for incidents that occurred in other jurisdictions; 24 women told nurses that they had called police when they hadn’t; and victims’ names were duplicated in six of the cases. In an additional eight cases, no hospital exam was given despite assertions by the rights group.

Crowell & Moring said police found documentation for all but five of the remaining sexual assault complaints.

“We determined that not only were investigations conducted in most of those cases, but many of the investigations resulted in arrests,” the report said. But: “In some cases, the investigation was admittedly inadequate.” D.C. police said they have reopened three of those cases.