The mass arrests of protesters in 2000 and 2002 cost the District nearly $22 million in court settlements and prompted a new law regulating how police investigate groups exercising their free speech rights.

But the office of the D.C. auditor, trying for the first time to assess whether District police have fully complied with the 2004 law, said it was stymied by the department’s refusal to turn over un-redacted e-mails from undercover officers.

As a result, the auditors said in a report to be released Friday that they have no idea how police monitored, investigated and possibly infiltrated organizations planning demonstrations in the nation’s capital.

Such information, the chief auditor said in her conclusion, “would have increased public trust and confidence” in the police force. The report was obtained by The Washington Post.

The review also accuses police of other failings, including launching sensitive investigations without proper authorization and oversight, which D.C. Police Chief Cathy L. Lanier vehemently denied in her written response, which was also obtained by The Post.

In a letter to the auditor, Lanier said the department would implement the 13 recommendations to tighten oversight. But she also offered a stinging rebuke, saying one auditor’s conflict of interest meant the panel could not be trusted with sensitive information and e-mails about undercover investigations.

Lanier said that in most if not all cases, her agency exceeded the law’s requirements but apparently failed to do so “to the satisfaction of the standards utilized by the D.C. Auditor.” She faulted the audit office for failing for six years to conduct an annual review and then critiquing her agency and holding it “to a higher standard based solely on criteria utilized by the auditor.”

A D.C. police spokeswoman referred inquiries to the response to the report. D.C. Auditor Yolanda Branche declined to comment ahead of the report’s release.

The 2004 law enacted by the D.C. Council was designed to instill oversight on a police force that detained more than 850 protesters during demonstrations in 2000 near the World Bank and International Monetary Fund buildings, and two years later in Pershing Park, again targeting the World Bank.

Two class action lawsuits resulted in multimillion dollar payouts. A federal judge in 2010 noted the new law, saying it would protect “future generations” for speaking out in public.

The law governs how police react to protests, forbidding them from encircling groups if they lack probable cause to arrest them, and in how detectives investigate the groups before they even hit the streets.

Art Spitzer, an attorney in the Washington office of the American Civil Liberties Union, said compliance is important, even on issues involving seemingly minor paperwork.

“The procedural safeguards are put in place for a very important reason,” Spitzer said. “Law enforcement has a tendency to see boogeymen where there really is only First Amendment activity.”

Investigating groups, Spitzer said, is sometimes necessary to ensure they also aren’t involved in criminal activity. But he said the threshold must be high.

“It requires sensitive decision making at a high level,” he said. “Failure to comply is not just a technical foul when there is real danger of infringing on First Amendment rights. There may be good reasons for a cop to be poking around, but presumably people at a higher level have better judgment about this than some undercover cop who is enthusiastic about doing his job.”

The audit office found deficiencies that included no authorization for 16 of 20 investigations into groups, and no written approval for use of undercover officers in 17 inquiries.

The auditors said police were “unable to produce written evidence that the Chief of Police had formally and in writing designated her authority to authorize the use of undercover officers.”

While the report also notes that her authority is not necessary, the auditors concluded that without something in writing, the team could not verify whether the investigations were proper.

The auditors recommend that police develop a procedure to put approvals in writing.

In her response, Lanier said her agency was being held to a higher standard than that of the law. In a point-by-point rebuttal, the department says that “the Intelligence Branch has consistently gone far beyond what is required” in seeking approval for its operations.