Updated

A key whistleblower in the Operation Fast and Furious scandal -- after being initially sidelined at the Bureau of Alcohol, Tobacco, Firearms and Explosives upon coming forward -- has been cleared by his ATF bosses and is now being hailed for the "essential role" he played in exposing the program.

ATF Special Agent John Dodson was cleared of wrongdoing pertaining to two internal investigations, according to a letter from Deputy Director Tom Brandon. Excerpts of that letter were released by Sen. Charles Grassley, R-Iowa, and Rep. Darrell Issa, R-Calif.

Brandon, according to the excerpts, praised Dodson for his role in bringing the botched anti-gunrunning operation to the attention of Congress.

"I fully appreciate that you took the courageous step of going to Congress to ensure that the public learned of the flawed tactics used in Operation Fast and Furious," Brandon said, adding that he played an "essential role" in holding others at ATF accountable.

"Although it took some time, the basic truth is now known to all: Throughout Operation Fast and Furious, agents and prosecutors failed to ensure that firearms were interdicted from straw purchasers and traffickers whenever there was a legal basis and opportunity to do so," he wrote.

The letter comes after an inspector general report last fall faulted a range of federal agencies for the program and accused officials in charge of a "disregard" for public safety.

Fast and Furious allowed weapons to "walk" across the U.S.-Mexico border and resulted in hundreds of firearms turning up at crime scenes in both countries. Guns from the operation were found at the scene of Border Patrol agent Brian Terry's murder.

In 2011, Dodson took his own complaints about the program outside the agency and went to Grassley. Yet after coming forward, he was transferred out of the ATF Phoenix office -- he moved to work at the South Carolina office.

His former chain of command also filed a complaint against Dodson for allegedly lying.

In their letter Tuesday to ATF Acting Director B. Todd Jones, Grassley and Issa said they were "pleased" with the deputy director's findings.