PETE YOST, Associated Press

WASHINGTON (AP) — Attorney General Eric Holder clashed Thursday with congressional Republicans seeking more information about a flawed gun-trafficking investigation in Arizona.

Lawmakers at a House Judiciary Committee hearing asked Holder what he knew in advance of public disclosure of a so-called gun-walking tactic in early 2011. As part of Operation Fast and Furious, agents were told to forego immediate arrests of suspected straw purchasers of guns and instead try to track the guns to higher-ups in gun-smuggling rings. Such a tactic is normally barred under Justice Department policy.

Agents lost track of hundreds of guns which flowed south to Mexico, where many were recovered at crime scenes. Two such guns were found in the U.S. at the scene of the killing of border agent Brian Terry.

Holder told the committee he became aware of the gun-walking tactic at the same time as the public and that he found out “about the same time” that guns found at the scene of Terry’s death were part of Operation Fast and Furious.

Holder has faced off repeatedly with Issa and other Republicans in recent months over his handling of the aborted firearms investigation. Issa’s committee has prepared a contempt citation against Holder but not voted on it yet, applying pressure for more documents on Operation Fast and Furious.

Holder said the Justice Department has cooperated fully with congressional investigators and turned over 7,600 pages of material to Congress about the operation.

“Look, I don’t want to hear about the 7,600,” snapped Rep. Darrell Issa, R-Calif. Chairman of the House Oversight and Government Reform Committee that is investigating the operation, Issa has been Holder’s frequent sparring partner during recent gun-walking hearings.

Issa said Thursday that wiretap applications in Operation Fast and Furious indicate that a number of key individuals at the Justice Department were responsible for the use of the gun-walking tactic.

“I’ve read them,” replied Holder, adding that he disagreed with Issa’s conclusions. The material on the wiretaps is sealed in a federal court, but Issa said the committee obtained the applications from whistleblowers cooperating with his investigation.

Gun-walking has long been barred by Justice Department policy, but was used in the Arizona operation in an effort to dismantle entire arms-trafficking networks and reach kingpins who had long eluded prosecution. Previous law enforcement strategy had focused on prosecuting low-level illicit arms buyers at the bottom of the chain, but that allowed thousands of weapons to reach Mexico. The gun-walking tactic was first used in two similar operations during the George W. Bush administration.

Committee chairman Lamar Smith of Texas asked for the identity of the highest-level official in the Obama administration who knew gun-walking was taking place. Holder replied that the operation began in law enforcement offices in Arizona and that he was not at all certain beyond that.

I don’t think anybody in Washington knew about those tactics,” said the attorney general.

The Justice Department’s inspector general is looking into who knew.

“How many people in Mexico have been killed as a result of the U.S.” engaging in the gun-walking tactic? asked Rep. Ted Poe, R-Texas.

“I don’t know, but I think there would be some,” replied Holder. The attorney general pointed to a broader picture: That 68,000 guns recovered by Mexican authorities in the past five years have been traced back to the United States. Operation Fast and Furious involved about 2,000 guns in total, and agents lost track of about 1,400 of those.

At Thursday’s hearing, House Democrats placed on record letters urging Issa not to pursue Holder’s contempt citation. The letters included notes from Philadelphia Police Commissioner Charles Ramsey, the National Organization of Black Law Enforcement Executives, the survivors of the mass shooting in Tucson that wounded former Rep. Gabrielle Giffords and the National Action Network headed by the Rev. Al Sharpton.