Inspector General Michael Horowitz. (AP)

(CNSNews.com) – The White House’s refusal to release communications related to the Fast and Furious gun-walking program and the refusal of a White House official to be interviewed about the matter “made it impossible” for the inspector general (IG) of the Justice Department to “pursue that aspect of the case,” the IG, Michael Horowitz, testified.

He added that the sought-after White House interview and communications constituted “a lead we wanted to follow.”

At a hearing of the House Government Reform and Oversight Committee on Thursday, Rep. Blake Farenthold (R-Tex.) asked Horowitz, “You noted also in your report that the White House refused to share internal communications with you during your investigation of Fast and Furious. We've noted a connection into the White House through Kevin O'Reilly at the National Security Council. Do you think the White House’s refusal to share these documents limited the scope of your investigation? Would this committee be well served by pursuing an investigation into that avenue?”

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Horowitz answered, “Well, as we noted in the report, and as you know, congressman, we did not get internal communications from the White House and Mr. O’Reilly’s unwillingness to speak to us made it impossible for us to pursue that angle of the case and the question that had been raised."

Farenthold: "So it would probably be worthwhile for us to pursue?"

Horowitz: "Well, certainly we have sought to pursue every lead we could. So, I can tell you, from our standpoint it was a lead we wanted to follow.”

The report, A Review of ATF’s Operation Fast and Furious and Related Matters, was released yesterday by the office of the inspector general.

Mr. O’Reilly is Kevin O’Reilly and when Fast and Furious was in operation he was a member of President Barack Obama’s National Security Staff.

The IG report states, “We also sought to interview Kevin O’Reilly, an official with the White House National Security Staff, about communications he had in 2010 with Special Agent in Charge William Newell that included information about Operation Fast and Furious. O’Reilly declined through his personal counsel our request for an interview.”

Bill Newell was the ATF Special Agent in Charge for the Phoenix, Ariz., office that was running Operation Fast and Furious.

The IG report says, “We sought to interview O’Reilly in light of e-mail communications he had with Special Agent in Charge Bill Newell in 2010.”

Former ATF Special Agent in Charge Bill Newell. (AP)

“Newell told us that he had known O’Reilly during previous field office assignments and that the two shared information about firearms trafficking issues relevant to their geographic areas of responsibility,” the report said. “According to Newell, O’Reilly was also friends with ATF’s White House Liaison and through that relationship O’Reilly would be included on some information sharing between Newell and the ATF Liaison about ATF’s efforts on the Southwest Border, and that O’Reilly eventually communicated with Newell directly.”

Operation Fast and Furious was run by the ATF (Bureau of Alcohol, Tobacco, Firearms and Explosives), which is overseen by the Department of Justice, headed by Attorney General Eric Holder. The program, which ran from the fall of 2009 to mid-December 2010, allowed guns to “walk” into the hands of Mexican drug cartels through straw purchasers.

Attoney General Eric Holder. (AP Photo/Bill Haber)

More than 2,000 firearms, largely AK-47s and 5.7 caliber pistols, were sold and allowed to walk. The ATF recovered only about 100 of the 2,000-plus weapons. In January 2010, a straw purchaser, Jaime Avila – well known to the ATF -- bought three AK-47s at a Phoenix-area gun store. Two of those weapons were later found at the murder scene of U.S. Border Patrol Agent Brian Terry on Dec. 14, 2010.

After Terry’s death, Operation Fast and Furious was halted and Avila was arrested.

At the hearing on Thursday, Committee Chairman Darrel Issa (R_Calif.) asked Inspector General Horowitz: “Kevin O’Reilly. Could you tell us a little bit about your effort to reach out to Kevin O’Reilly, a member of the White House national security team?

Horowitz said: “We reached out to his lawyer, requested an interview. We have no basis to compel interviews from individuals who work outside the Department of Justice. He was not working in the Department of Justice so we had to ask for a voluntary interview and he denied ….”

Issa: “Would it surprise you he’s been in Afghanistan. We’ve been denied.”

Horowitz: “I was not aware of where he was.”

Issa: “I’m sorry, it was Iraq [not Afghanistan].”

Horowitz: “I don’t recall knowing myself where he was, but we were told by his council that he would not [grant an interview].”

Rep. Darrell Issa (R-Calif.), chairman of the House Oversigh and Government Reform Committee (AP Photo)

The House Oversight and Government Reform Committee has been seeking to interview O’Reilly for more than year. According to CBS News, the White House disclosed in the fall of 2011 that O’Reilly had been reassigned from the National Security Staff to a position with the State Department in Iraq.

O’Reilly’s attorney reportedly said that his client would agree to a telephone interview with the committee but only if the White House said okay. White House Counsel Kathryn Ruemmler has stated that O’Reilly will not be permitted to give an interview.

CBS reported, “citing Executive Branch confidentiality interests, Ruemmler said, ‘There is an insufficient basis to support the request to interview Mr. O'Reilly.’”

Michael W. Chapman contributed to this report.