Assistant Attorney General Lanny Breuer became the first high-ranking official Tuesday to admit that he knew U.S. agents were letting thousands of guns sold in the U.S. fall into the hands of Mexican drug cartels.

But Breuer says the controversial “gun walking” tactics he learned about in April 2010 weren't part of “Operation Fast and Furious,” but rather a previous investigation during the Bush administration called “Wider Receiver.”

Appearing before a Senate Judiciary subcommittee Tuesday, Breuer said he made a mistake by not speaking up about what he knew – even after ATF whistleblowers went public about Fast and Furious and were blasted for lying.

“I regret that in April of 2010 that I did not draw the connection between 'Wide Receiver' and 'Fast and Furious,' and moreover I regret that even earlier this year I didn’t draw that connection," he said.

Wide Receiver was an operation during the Bush administration similar to Fast and Furious under the Obama administration where illegally purchased weapons entered Mexico instead of being stop by ATF. Under Wide Receiver, which ran from 2006 to the end of 2007, the ATF recruited a gun dealer to sell some 450 assault rifles to known straw buyers and then watched as many of those guns crossed the Mexican border.

Under Fast and Furious, more than 2,000 illegally purchased guns were not tracked, with many crossing into Mexico. Public outcry over Fast and Furious was ignited when Border Patrol Agent Brian Terry was gunned down last December. Two of the guns recovered at the scene were later traced to Fast and Furious.

Some lawmakers find Breuer’s story implausible because he learned about Wider Receiver at the same time as Fast and Furious, run by the same agents and the same U.S. attorney’s office.

“He was asking questions about Wide Receiver at the very same time Fast and Furious was going on and it was going on in the same division within the Justice Department, so why wouldn’t they be asking questions about Fast and Furious the same way as they were about Wide Receiver?” Grassley told Fox News.

Documents released Monday show Breuer and others knew about Wide Receiver last year.

“Been thinking more about ‘Wide Receiver,’” Deputy Attorney General Jason Weinstein wrote in April 2010. “ATF headquarters should/will be embarrassed that they let this many guns walk – I’m stunned.”

Holder said months ago this never reached into the upper levels of the Justice Department. Next week Holder will face questions from the Senate Judiciary Committee about his level of involvement with Fast and Furious.

As the Fast and Furious investigation enters its 10th month, the blame game grows more intense.

“In this investigation, best of my knowledge, we didn’t let guns walk,” said Phoenix Chief Bill Newell.

Newell testified he did nothing wrong, the former ATF director said he never read his memos. Holder claims he didn’t know about the operations’ “questionable tactics.”

And while more than two dozen congressmen now want Holder’s resignation, others say they just want a little honesty.

“Lanny Breuer’s statement said he told the attorney general in January or February so that doesn’t jive,” said Sen. John Cornyn, R-Texas. “So we’ve just got some massive contradictions here.”

The documents that were released Monday lay much of the blame on a U.S. attorney who said he had no ‘chargeable offenses’ – even though 600 guns were already illegally bought. He also claimed the ATF never purposely walked guns, even though agents testified they did.