"Gunwalker" allegation: ATF target was FBI informant

Tuesday: The aftermath of Irene has completely cut off 13 towns in Vermont, leaving them without water and no way to escape; Also, unable to distance themselves from the Gunwalker scandal, top ATF officials are being removed from their positions; And, CBS News obtained newly-released footage documenting FEMA's rescue efforts after 9/11.

Confidential sources have told Congressional investigators that a main target ATF was trying to identify in Fast and Furious was actually a DEA confidential informant working with the FBI.

That twist is just part of the new information included in a letter from Sen. Charles Grassley (R-Iowa) and Rep. Darrell Issa (R-CA) addressed directly to Attorney General Eric Holder, who has indicated he neither knew of nor approved of the "gunwalking" operation that allegedly allowed thousands of weapons to be sold to suspected traffickers for Mexican drug cartels.

According to Grassley and Issa, if the DEA and FBI had shared information with ATF, "then Operation Fast and Furious may have ended as many as ten months sooner than it did. This would have prevented hundreds of assault-type weapons from being illegally straw purchased on behalf of Mexican drug cartels."

Gunwalker probe points to DOJ

The letter outlines an amazing alleged failure of DEA and FBI to share crucial investigative information with ATF.

It says while ATF was trying to identify the unnamed financier behind a gun trafficking ring leader named Manuel Celis-Acosta, the DEA and FBI already knew who the financier was - and had in fact turned him into a confidential informant. Yet, the letter states, the financier was allowed to continue to purchase weapons from Acosta over the course of a year, without ATF ever knowing that the man they were seeking to identify... was a government informant.

ATF Fast and Furious secret audio recordings

The letter also states that prior to becoming a confidential informant, the financier may have used $3,500 in taxpayer money, "official law enforcement funds," to finance weapons trafficking. He allegedly received the money - not knowing it came from the U.S. government -- by selling narcotics to another government confidential informant.

The Justice Department had no immediate comment.

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    Sharyl Attkisson is a CBS News investigative correspondent based in Washington.