A conservative congressman today called on Attorney General Eric Holder to resign after new revelations surfaced about his knowledge of the botched Fast and Furious gun-running operation. Beginning in July 2010, Holder received at least five memos about the flawed operation, but told Congress this May he had just learned of Fast and Furious weeks earlier.

“As our nation’s top enforcer of the principles of law and justice, Mr. Holder has lost all credibility and should step down immediately,” Rep. Raúl Labrador said in a statement this afternoon.

Holder testified before the House Judiciary Committee on May 3, ducking responsibility for Fast and Furious. The operation, carried out by Bureau of Tobacco, Firearms and Explosives, put guns in the hands of straw buyers, who then gave the firearms to Mexican drug cartels. One of those guns was found at the murder scene of U.S. Border Patrol Agent Brian Terry.

House Oversight Chairman Darrell Issa (R-CA) and Sen. Chuck Grassley (R-IA) have led the congressional inquiry and today announced that Holder knew more about Fast and Furious than he acknowledged at the May 3 hearing. In fact, Holder received memos about the operation for four straight weeks last year from Michael Walther, director of the National Drug Intelligence Center.

Those memos revealed to Holder that straw buyers were “responsible for the purchase of 1500 firearms that were then supplied to Mexican drug trafficking cartels.”

“Attorney General Holder has failed to give Congress and the American people an honest account of what he and other senior Justice Department officials knew about gunwalking and Operation Fast and Furious,” Issa said. “The lack of candor and honesty from our nation’s chief law enforcement officials in this matter is deeply disturbing.”

The lack of honesty didn’t sit well with Labrador, who first requested a hearing on Fast and Furious in March after learning about the flawed operation from his constituents.

“Attorney General Holder has a troubling pattern of failed cooperation with the legislative branch. Because of this intentional stonewalling and his misleading testimony, I now call for Mr. Holder’s resignation,” Labrador said. “It is clear he has not been honest about the extent of his involvement with the failed Fast and Furious program and should not be entrusted with managing the Department of Justice.”