Justice Department officials announced Tuesday that they had reassigned the ATF director and that the U.S. attorney in Phoenix had stepped down, a major shake-up in response to the controversy over a Phoenix-based U.S. gun-trafficking operation.

Kenneth E. Melson, acting director of the Bureau of Alcohol, Tobacco, Firearms and Explosives, will become a senior adviser on forensic science at the Justice Department’s headquarters in Washington. Dennis Burke, the U.S. attorney in Phoenix, will leave the department, and one of his prosecutors has been reassigned.

The changes follow months of investigations into the agency’s “Operation Fast and Furious.” That now-defunct initiative, which focused on Mexican gun traffickers, resulted in a congressional inquiry after a U.S. Border Patrol agent was killed in an incident in which Fast and Furious guns were found at the scene.

Law enforcement officials said the personnel moves were the Justice Department’s answer to accusations from congressional Republicans, who have blasted the operation and are pushing to learn whether senior Justice officials in Washington were involved.

Before his resignation, Burke took full responsibility for Fast and Furious in testimony to congressional investigators that was released by House Democrats on Tuesday. “When our office makes mistakes, I need to take responsibility,” he said on Aug. 18. “This is a case . . . it should not have been done the way it was done, and I want to take responsibility for that, and I’m not falling on a sword or trying to cover for anyone else.”

But the personnel moves failed to satisfy the department’s critics on Capitol Hill, who vowed to continue their investigation of Fast and Furious and suggested that other senior officials could be held responsible. The Justice Department’s inspector general is also investigating, at the request of Attorney General Eric H. Holder Jr.

Rep. Darrell Issa (R-Calif.), chairman of the House Committee on Oversight and Government Reform, said the changes were “warranted,” but he added that the committee “will continue its investigation to ensure that blame isn’t off-loaded on just a few individuals for a matter that involved much higher levels of the Justice Department.’’

Although law enforcement officials said no further high-level changes are planned, Sen. Charles E. Grassley (R-Iowa), who is helping lead the congressional probe, said Tuesday that he “wouldn’t be surprised to see more fallout beyond the resignations and new assignments announced today.”

He called the announcements “an admission by the Obama administration that serious mistakes were made in Operation Fast and Furious.”

Melson, another senior ATF official and Burke have told congressional investigators that senior Justice officials were unaware of the tactics used in Fast and Furious.

Melson will be replaced at ATF by B. Todd Jones, the U.S. attorney in Minnesota. Burke, who worked closely with ATF and whose office gave legal backing for Fast and Furious, is being replaced on an acting basis by his deputy, Ann Scheel. Emory Hurley, an assistant U.S. attorney in Phoenix who helped oversee the gun-trafficking operation, is being transferred from the office’s criminal division to its civil division, meaning he will not be involved in criminal cases.

No explanation

Justice Department officials, in their public statements, did not explain the personnel moves. Holder described Jones as “a seasoned prosecutor and former military judge advocate . . . who brings a wealth of experience” to the ATF job.

Jones will remain U.S. attorney in Minnesota while serving in an acting capacity at ATF. The agency has been without a permanent director since 2006, when Congress required the position to be confirmed by the Senate.

President Obama in November nominated Andrew Traver, special agent in charge of ATF’s Chicago field division, to head the agency. But the National Rifle Association strongly opposes Traver, and his nomination has stalled in the Senate.

Melson, a longtime Justice Department official, conceded in congressional testimony that his agency made mistakes in overseeing Fast and Furious, which critics consider the agency’s biggest debacle since the deadly 1993 Branch Davidian confrontation in Waco, Tex. ATF is part of the Justice Department.

Melson had made his own changes in response to the investigations, reassigning three ATF officials involved in Fast and Furious, including the former head of the Phoenix office, William Newell.

Officials described Melson’s departure from ATF as a mutual decision. They said he is happy with his new role and that forensic science has been a longtime passion of his. “He was very pleased with the way he was treated,” said Melson’s attorney, Richard Cullen.

Burke, who became U.S. attorney in Phoenix in September 2009, had also been overseeing the prosecution of Jared Lee Loughner in the mass shooting in Tucson that killed six and wounded 13, including Rep. Gabrielle Giffords (D-Ariz.). It is unlikely that his departure will affect that case.

Holder on Tuesday praised the office’s “quick response” to the January shooting, along with Burke’s “unwavering commitment to the Department of Justice.” The attorney general’s statement did not mention Fast and Furious.

Following the guns

In that operation, agents tried to follow the paths of guns, from illegal buyers known as “straw purchasers” through middlemen and into the hierarchy of the powerful Sinaloa drug cartel. It was a key part of the Obama administration’s strategy for combating the deadly Mexican cartels, though Obama has said that he and Holder would never have allowed the tactics used in Fast and Furious.

On Dec. 14 of last year, Border Patrol agent Brian Terry and other officers were patrolling a canyon in the Arizona desert when they got into a firefight with five suspected illegal immigrants.

Terry was fatally shot in the melee. Investigators made four arrests and found two AK-47 semiautomatic rifles near the scene. The serial numbers on the rifles matched those on guns bought outside Phoenix by a Fast and Furious suspect a year before. The bullet that killed Terry was so damaged that neither of the firearms could be definitively linked to his killing, according to a law enforcement official.

It was later revealed that the Fast and Furious operation had allowed more than 2,000 weapons to hit the streets, a fact that helped prompt the congressional probe.

Rep. Elijah E. Cummings (Md.), the top Democrat on Issa’s committee, said the departures of Melson and Burke will give ATF “fresh leadership” that will allow it “to move forward and focus on its vital mission of enforcing our nation’s gun laws.”

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