Department of Veterans Affairs Acting Inspector General Richard Griffin,on Capitol Hill in Washington in 2014. (AP Photo/Manuel Balce Ceneta)

The chief watchdog for the Department of Veterans Affairs announced Tuesday that he is retiring this week after months of criticism that his office failed to aggressively investigate wrongdoing in the troubled agency.

Richard Griffin, who has served as acting inspector general since 2013, had come under fire from members of Congress, whistleblowers and veterans’ groups for being too cozy with leaders of the agency that his office is supposed to investigate for fraud, waste and abuse.

[Lead investigator of wait times at VA still gets criticism over report ]

His departure, first reported by USA TODAY and Military Times, comes a day after a group of whistleblowers from VA medical clinics and hospitals around the country wrote a letter to President Obama urging him to fire Griffin, calling the inspector general’s modus operandi a “horrifying pattern of whitewashing and deceit.”

In announcing Griffin’s departure on its Web site, the inspector general’s office said that in the past six years it has issued almost 2,000 reports and conducted investigations that led to more than 11,000 arrests, indictments, convictions and administrative sanctions.

“Your collective effort and hard work have resulted in a remarkable record of performance and outstanding achievements,” Griffin told his staff, according to the announcement.

But he had faced criticism repeatedly since last fall. As the lead investigator looking into long wait times for veterans seeking health care, Griffin concluded he was “unable to conclusively assert” that delays at the Phoenix VA Health Care System had caused patients to die.

That finding turned him  into a lightning rod at the center of the biggest scandal in VA’s history. He became a target for the anger and frustration of veterans groups, VA medical staff and members of Congress who say his report, released last August, was a whitewash.

Under pressure from critics, this spring Griffin released more than 140 investigations of veteran heath care across the country that his office had closed without issuing public reports. Some of them documented veteran deaths and harm.

“The VA Office of Inspector General is in desperate need of new leadership,” Danielle Brian, executive director of the Project on Government Oversight, said in a statement, “the kind of aggressive and independent oversight sorely lacking under Mr. Griffin’s tenure.”

“Instead of being a champion of whistleblowers, Mr. Griffin was part of the VA’s toxic culture of intimidation and retaliation,” she wrote.

Linda Halliday, the widely respected assistant inspector general for audits and evaluations, will take over the office starting next week.