WASHINGTON-Congressional lawmakers grilled U.S. Attorney General Eric Holder on Thursday, a year after the death of a federal agent occurred in the wake of a botched Justice Department gun operation.

Hundreds of weapons went missing in the program called Operation Fast and Furious. Republicans at Thursday's House Judiciary Committee hearing said questions remain as to why Justice Department officials permitted the operation of the dangerous plan.

"I am disappointed in the department's repeated refusal to cooperate with this committee's oversight requests," Rep. Lamar Smith, R-Tex., told Holder. "And inconsistent statements from department officials about who knew what and when have only raised more concerns. President Obama has promised an open and transparent government. Unfortunately, we often see a closed and secretive Justice Department."

Smith was not the only Republican to attack Holder in a heated hearing on a program that led to weapons failing into the hands of suspected Mexican drug smugglers.

"There is really no responsibility within the Justice Department," said Rep. Jim Sensenbrenner, R-Wis. "The thing is, if we don't get to the bottom of this … there is only one alternative that Congress has, and it is called impeachment."

Sensenbrenner engaged in a testy exchange with Holder about a February letter from the Justice Department to Congress that denied the existence of the gunrunning operation. Officials withdrew the letter recently due to inaccuracies, but Holder denied that Justice Department officials lied to Congress.

"Tell me what's the difference between lying and misleading Congress," Sensenbrenner asked Holder.

"It all has to do with your state of mind," Holder replied.

Fast and Furious allowed the sale of up to 2,000 guns to Mexican criminal organizations, with the intention of using the weapons to track the flow of firearms across the Mexican border. But the Bureau of Alcohol, Tobacco, Firearms, and Explosives failed to effectively coordinate with Mexican authorities, resulting in agents losing sight of the weapons.

Investigators found two of the guns at the December 2010 crime scene of the shooting death of Customs and Border Patrol Agent Brian Terry.

Holder, who testified earlier this year that he learned of the program only in spring 2011, called the operation misguided and inexcusable on Thursday. He said it is a tactic that "must never happen again."

But Holder claimed that top Justice Department leaders were not informed of the operation until the tactics were made public. He also blamed partisan divisions and "politically motivated gotcha games" for driving the ongoing congressional investigation.

"We cannot afford to allow the tragic mistakes of Operation Fast and Furious to become a political sideshow or a series of media opportunities," Holder told lawmakers at the hearing.

Rep. Darrell Issa, R-Calif., continued to go after Holder, questioning the attorney general about why no one has been held accountable for not stopping a project "failed and flawed from the beginning." Issa added, "Mr. Attorney General, the blame must go to your desk."

With five boxes stacked up to his right representing evidence received from a gun dealer and just one box on his left representing the documents handed over to the congressional committee by the Justice Department, Issa wondered why none of the 5,000 emails released by the department so far include emails to or from the attorney general.

"Does it cause you to think that in fact we believe that you are withholding documents," Issa asked Holder, who leaned back in his chair with a look of dismay.

One day earlier, Sen. Charles Grassley, R-Iowa, called for the resignation of a top Holder lieutenant. During a speech on the Senate floor, Grassley, a senior member of the Senate's Judiciary Committee, said Lanny Breuer, an assistant attorney general who oversees criminal matters at the Justice Department, failed to act after learning about Fast and Furious.

Grassley also accused Breuer of misleading lawmakers during congressional testimony earlier this year. "It just isn't credible that someone like Mr. Breuer would forget about his involvement in a matter like this," said Grassley.

This call for Breuer's resignation came after new records turned over by the Justice Departments show Breuer praising in an email the now withdrawn February letter to Congress that erroneously denied the existence of the gun program.

"Mr. Breuer has lost my confidence in his ability to effectively serve the Justice Department," Grassley said.

In the midst of all the verbal fireworks during Thursday's House hearing, Holder gave the most sobering comment when he admitted that more of the lost guns from Fast and Furious would surface.