A senior U.S. senator is seeking to remove the Justice Department's internal watchdog from an investigation into allegations that the Bureau of Alcohol, Tobacco, Firearms, and Explosives (ATF) allowed thousands of illicit weapons to flow to Mexico, possibly leading to the death of a Border Patrol agent.

Sen. Chuck Grassley of Iowa, the top Republican on the Judiciary Committee, said Wednesday he lacked confidence in the Justice Department inspector general's office to produce a report that the public would view as "frank and unbiased."

"There are certainly better and more independent ways to conduct this investigation," Grassley said in a letter to Kevin Perkins, the head of the Integrity Committee of the Council of Inspectors General on Integrity and Efficiency. "The fact that the inspector general did not take this whistleblower's allegations seriously enough to even call him back raises a lot of red flags for me."

After the murder of Border Patrol Agent Brian Terry in December, ATF agent and whistleblower John Dodson alleged that a joint task force headed by the ATF and the Justice Department known as Project Gun Runner allowed thousands of weapons to be illegally trafficked to Mexico without making arrests of known smugglers.

Records show Gunrunner was aware of more than 1,000 weapons sold from 10 Arizona gun stores to roughly 50 straw buyers. More than two thirds of those guns have already been recovered at crime scenes in the U.S. and Mexico.

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"What people don't understand is how long we will be dealing with this," Dodson said. "Those guns are gone - -gone. You can't just give the order and get them back. There is no telling how many previous crimes will be committed before we get to them."

The National Rifle Association (NRA) sent a letter to Grassley and Sen. Patrick Leahy, D-Vt., the chairman of the Judiciary Committee, asking for expedited hearings on ATF's firearms trafficking strategies.

"We are clearly at a critical point on this issue," the NRA wrote in the letter. "Without aggressive enforcement of existing laws, the situation on the border will continue to deteriorate, claiming the lives of innocent citizens and law enforcement personnel alike. Yet reckless enforcement tactics may already have cost lives, while ineffective regulatory requirements would waste scarce resources and undermine Americans' Second Amendment rights."

ATF announced last week that it has asked a panel of law enforcement professionals to review its current firearms trafficking strategies.

"It will support the goals of ATF to stem the illegal flow of firearms to Mexico and combat firearms trafficking in the United States, "ATF Acting Director Kenneth Melson said in a written statement.

The weapons used to kill Terry were being tracked by Gunrunner. Grassley said he began looking into allegations brought forward by Dodson and more than a dozen other ATF agents after the Justice Department inspector general failed to investigate.

Grassley cited that reason for asking for another inspector general's office to conduct the review. He also cited the current vacancy of the inspector general and a report issued by the office that was critical of Gunrunner that he says led to a shift in strategy of allowing guns to cross the border.

The inspector general "may be sensitive to the appearance that its previous criticism created the conditions under which ATF and DOJ felt pressured to take risks in order to make a 'big case' against the cartels," Grassley wrote. "Again, that could create an incentive to minimize the significance of the allegations.