D.C. Council Chairman Phil Mendelson was asked in 2010 to review allegations that the Metropolitan Police Department deliberately understated the number of sexual assaults in the city, a letter obtained by The Washington Examiner shows, but he chose not to launch the formal investigation the police union demanded.

"Not only did the department fail to take proactive steps to address the rising number of sexual assaults, but it worked to actively conceal the increase from the public," Kristopher Baumann, chairman of the labor committee of the D.C. chapter of the Fraternal Order of Police, wrote to Mendelson.

Mendelson led the council committee that oversees the MPD at the time of the letter, which came amid persistent questions about department-generated crime statistics.

Mendelson said he did not believe he had disregarded "qualitative" problems and said he asked the MPD about allegations of statistical "game-playing."

"We didn't ignore the letter," Mendelson said. "We inquired of MPD and what they were doing and how they were handling the data."

But Baumann strongly disagreed and had harsh words for Mendelson.

"He's a hypocrite for coming out and telling the public that he was concerned about this," said Baumann, who also criticized Mendelson's "complete failure to exercise oversight."

Baumann's letter surfaced weeks after Human Rights Watch alleged that the MPD failed to investigate at least 170 sexual assaults.

Police Chief Cathy Lanier has criticized the group's findings as dependent on flawed research by an organization more intent on garnering publicity for itself than helping crime victims.

The D.C. Council is investigating the report's allegations, but Mendelson contended that Baumann's renewed critiques of city leaders were merely efforts to take advantage of another group's high-profile investigation.

"The FOP president is just seeing this as another opportunity to beat up on the chief," Mendelson said. "The union has been very critical of command. They have not been critical of line officers. They don't criticize themselves, and the Human Rights Watch report criticisms apply as much to the front-line officers as they do to the command staff."

And Lanier, who has argued that her agency's efforts to reach out to more victims prompted the increase in reports, said Baumann's charges would only dilute public trust in law enforcement.

"As I stated then -- and the chairman of the FOP as a police officer knows -- sexual assault is historically an underreported crime," Lanier said in an email. "The allegations from HRW and the police union will only serve to discourage victims of sexual abuse from reporting their abuses to the police."

Baumann disputed those assertions.

"We tried to get the department to address these issues three years ago," he said. "If the department had listened to us, we wouldn't be having this conversation right now."