Ryan J. Reilly December 6, 2011, 5:35 AM

Rep. Darrell Issa (R-CA) on Monday expanded his investigation into why ATF let guns “walk” across the Mexican border during Operation Fast and Furious, to include a probe of DEA laundering money to Mexican drug cartels.

The New York Times reported on Sunday that U.S. narcotics agents “have laundered or smuggled millions of dollars in drug proceeds as part of Washington’s expanding role in Mexico’s fight against drug cartels.”

Issa brought up the issue in the context of his Fast and Furious probe in a letter to Attorney General Eric Holder, who is appearing before the House Judiciary Committee on Thursday.

“The existence of such a program again calls your leadership into question,” Issa said in the letter. “The managerial structure you have implemented lacks appropriate operational safeguards to prevent the implementation of such dangerous schemes. The consequences have been disastrous. It is almost unfathomable to contemplate the degree to which the United States Government has made itself an accomplice to the Mexican drug trade, which has thus far left more than 40,000 people dead in Mexico since December 2006.”

But former DEA officials, according to the New York Times, “rejected comparisons between letting guns and money walk away. Money, they said, poses far less of a threat to public safety. And unlike guns, it can lead more directly to the top ranks of criminal organizations.”

Robert Mazur, a former DEA agent who authored a book on his years as an undercover agent in Colombia, told the NYT that drug kingpins were “super-insulated” and that the “only way to get to them is to follow their money.”

Issa has requested a briefing for his staff on the issue before 5 p.m. on Wednesday.

Drug Enforcement Agency, Eric Holder, Fast And Furious