New details about Operation Fast and Furious cast doubt on the ability of the Justice Department’s Office of Inspector General to conduct an “independent” and fair investigation, congressional Republican investigators say.

The information comes via a letter Sen. Chuck Grassley and Rep. Darrell Issa sent to Attorney General Eric Holder on Tuesday. In it, they question a request from Holder for a transcript from a meeting they held in secret on July 4th with Ken Melson, acting director of the Bureau of Alcohol, Tobacco, Firearms and Explosives.

Holder apparently told Issa and Grassley he was requesting the transcript for the DOJ and for the Office of the Inspector General — the entity that’s supposed to be distinct enough from Holder’s office to conduct a fair Operation Fast and Furious investigation.

Holder and other DOJ officials have repeatedly said the DOJ’s Inspector General is conducting its own internal investigation into what went wrong with Fast and Furious. Even so, Holder’s latest request on behalf of the OIG sparks skepticism from investigators in Congress.

“Since the OIG is supposed to be conducting an independent inquiry, it seems odd that the Department would make a document request on behalf of that office,” Grassley and Issa wrote to Holder on Tuesday. “We presume that if the OIG would like to make such a request, it is capable of doing so on its own initiative. However, we have not received any such request from the OIG.”

In their Tuesday letter, Grassley and Issa also ask Holder to provide complete and full answers to all of the questions they sent him on July 22. Issa and Grassley say Holder failed to do so in his most recent response.

They say “perhaps the most troubling reply” Holder gave them was that the ATF did not have detailed information available on 11 instances ATF admits being aware of that Fast and Furious weapons were recovered inside the United States in “connection with violent crimes.” (RELATED: Issa, Democrats, NLRB fight spar over oversight committee document demands)

“The question specifically asked you to ‘describe the date and circumstances of each recovery [in the United States] in detail,’” the top Republican congressional investigators wrote. “However, the reply failed to do so.”

Issa and Grassley say Holder failed to provide an “enumerated response” when they asked him if the Deputy Attorney General’s office or any other DOJ agency was given a briefing paper outlining Fast and Furious’s mission. “Currently, our strategy is to allow the transfer of firearms to continue to take place,” the briefing paper read.

Issa and Grassley also point out that Holder’s response, that unnamed DOJ officials became aware of that briefing paper once the House Oversight Committee began investigating Operation Fast and Furious, didn’t answer their question.

“That may be true and somewhat related to the question, but it falls far short of being responsive,” they wrote. “Whether some unnamed DOJ officials may have learned of the briefing paper during the Congressional investigation in 2011 tells us nothing about which other officials at Department components outside ATF may have received the briefing paper in 2010.”