The former head of the U.S. Drug Enforcement Administration's high-profile office in Colombia has been cleared of wrongdoing following a probe of misconduct allegations, including accusations that he used government resources to hire prostitutes.

A DEA letter addressed to Richard Dobrich said the investigation turned up "no evidence to support this allegation" and was being closed.

Dobrich provided a copy of the Dec. 7-dated letter, which was signed by Preston Grubbs, the deputy head of the DEA, to The Associated Press. DEA spokeswoman Mary Brandenberger confirmed he had been cleared but declined further comment.

The Justice Department's Office of Inspector General had launched a probe into Dobrich, then the DEA's top-ranking official in South America, after receiving an anonymous complaint alleging he directed Colombian drivers working for the U.S. Embassy in Bogota "to procure sex workers," according to a copy of the complaint obtained by the AP.

Dobrich, a former Navy SEAL who was injured during a firefight with the Taliban during a counter-narcotics raid in Afghanistan in 2010, called the allegation an attempt at "character assassination," possibly by a disgruntled former DEA employee.

"I never dishonored the oath that I took and still care deeply about the DEA's mission and the people who work very hard to tackle serious issues," he said in an interview Monday, adding that he had filed a complaint with Colombian police that may allow them to uncover the author's identity.

He also expressed frustration that the anonymous complaint and word of the probe ever got out, saying it had caused harm to his family and reputation, and said DEA leadership should have done more to stand by him in the face of what he called an "obviously laughable accusation."

"They treated me like a leper," he said. "This is a great recipe on how to cause chaos in an office."

Dobrich said he has filed a grievance with the Justice Department, alleging undue delays in closing the case and clearing his name.

Dobrich's tenure as the top DEA executive in Colombia began in 2015, when he was brought in to restore order after a blistering Inspector General's report found several DEA agents had participated in "sex parties" with prostitutes hired by Colombian cartels. That scandal prompted the suspension of several agents and the retirement of Michele Leonhart, the DEA's administrator at the time.

Prostitution is legal in Colombia, but Justice Department policy forbids DEA agents from engaging in such activity because it could lead them to be compromised by the drug cartels they are pursuing.

"He would've had to been almost over the top stupid to have engaged in that kind of conduct considering the office's history," said Derek Maltz, a former agent who headed the DEA's special operations division.

Dobrich, 54, retired from the DEA in October after a nearly three-decade career to take a private sector job.

Prior to Bogota, he oversaw the DEA's military-style FAST teams that battled drug traffickers in Afghanistan and Latin America.

The DEA's Bogota office is critical to the U.S. efforts to control drug trafficking, and under Dobrich's tenure seizures of cocaine surged to an all-time high at the same time as cocaine production surged.

Maltz said he was saddened to see Dobrich leave the agency he spilled blood for on the terms he did.

"I have a lot of respect for his courage," Maltz said. "Unfortunately, there's a trend in government where we allow people who write anonymous letters to hurt people who have dedicated their entire life to public service."

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Mustian reported from New York.