FALLS CHURCH, Va. (AP) — At least 170 reported sexual assaults — and possibly more — went uninvestigated by the D.C. police department between 2008 and 2011, according to a long-awaited report from a human rights group.

The 197-page report from New York-based Human Rights Watch also found a pattern of callous behavior by D.C. police toward sex assault victims, with many saying they were actively discouraged from pursuing a criminal case.

Human Rights Watch said it was prompted to investigate the agency because federal crime statistics showed D.C. reported a suspiciously low number of rapes and sexual assaults.

Over the past few years, Human Rights Watch and the Metropolitan Police Department have engaged in high-profile exchanges, including a lawsuit by the watch group to gain access to police data.

Police Chief Cathy Lanier says her department has implemented reforms in years since Human Rights Watch first raised concerns. And she says she has doubts about the report's methodology.

The department "believes that objective outside observers will agree that HRW in its desire to draw public attention to themselves has used unsupported and erroneous information to attack MPD's handling of sexual abuse investigations," Lanier wrote in a Dec. 20 letter to the report's author, Sara Darehshori. The police department placed its correspondence with Human Rights watch on its website.

Darehshori said the data used in the report comes directly from the police department. And while she acknowledged that collecting the statistics was an arduous, time-consuming process, she is confident in her report's methodology and underlying data.

"We were very careful with the data," Darehshori said. "We gave police the benefit of the doubt" any time there was ambiguity in how the data could be interpreted.

A large portion of the report focuses on sexual assault cases that came in through Washington Hospital Center, where sexual assault victims are sent for forensic examinations.

The report concluded that of the 480 sexual assault complaints that originated at the Center between October 2008 and September 2011, police failed to file incident reports in 170 of those cases, or 35 percent.

The report says police policy requires officers to produce an incident report, and that a criminal investigation cannot be done without it.

An additional 34 cases, or 7 percent, had incident reports but were placed in an administrative category that closed the cases with minimal investigation.

The report also raises questions about whether the department is investigating complaints that come in through forums other than the hospital, though it lacks hard statistical evidence to prove reports aren't being filed in those circumstances.

The report also includes scores of interviews with people who filed complaints and felt they were treated badly, with some saying their experience with police was more traumatic than the sexual assault itself.

Kristopher Baumann, chairman of the D.C. chapter of the Fraternal Order of Police, said the allegations in the report fit a pattern over the years of the department manipulating reports to generate positive statistics.

"If you try to manipulate the numbers, those things will catch up to you," Baumann said. "It sounds like this report is going to be another embarrassment for the department."