A top Justice Department official knew that federal officials allowed assault guns and other weapons to fall into the possession of Mexican drug cartels as early as April 2010, 10 months before the department denied to Congressional investigators that the investigative strategy was used.

Documents show that Lanny Breuer, the assistant attorney general for the department’s criminal division, also received emails from his deputy about avoiding media scrutiny over the practice of letting the weapons “walk” in an effort to make more significant arrests. The documents were released Monday by the Justice Department to Congressional investigators and were obtained by Roll Call.

Breuer released a statement Monday expressing “regret” for not alerting other top officials about the tactic when it “became public.”

Two Republicans, House Oversight and Government Reform Chairman Darrell Issa (Calif.) and Senate Judiciary ranking member Chuck Grassley (Iowa), have been investigating Operation Fast and Furious, a weapons-smuggling investigation begun during the Obama administration by the Bureau of Alcohol, Tobacco, Firearms and Explosives. Whistle-blowers say the operation allowed hundreds of assault weapons and military-grade sniper rifles to cross the border into Mexico, which CBS first reported in February.

When first asked by Grassley in late January whether the tactic had been used in weapons-smuggling investigations, the Justice Department broadly denied that guns had been allowed to “walk” in a Feb. 4 letter.

“ATF makes every effort to interdict weapons that have been purchased illegally and prevent their transportation to Mexico,” Assistant Attorney General Ronald Weich wrote to Grassley at the time.

Breuer did not author the letter, and a senior Justice official said Monday that he did not participate in crafting it. The memos, emails and other documents released Monday show that Breuer learned in April 2010 that the ATF allowed guns to cross the border for Operation Wide Receiver, a similar, smaller-scale weapons-smuggling investigation begun during the George W. Bush administration.

Breuer was told about the tactic when his deputy, Jason Weinstein, became alarmed at the number of weapons that had been allowed to “walk” as part of Wide Receiver, which was conducted in 2006 and 2007.

Weinstein told colleagues in an April 12, 2010, email that the ATF should be “embarrassed that they let this many guns walk” in Wide Receiver.

“I’m stunned, based on what we’ve had to do to make sure not even a single operable weapon walked in [undercover] operations I’ve been involved in planning — and there will be press about that,” he wrote.

In a subsequent briefing to Breuer, Weinstein explained that “ATF let a bunch of guns walk in an effort to get upstream conspirators,” or snag higher-ranking criminals, according to an April 30 email recapping the meeting.

The Justice Department was preparing to launch its prosecution of suspects arrested under Wide Receiver, and Weinstein expected criticism when details of the investigation were made public as part of the court proceedings. He suggested that Justice wrap the public unveiling of Wide Receiver into a larger operation known as Deliverance to mask the “negative part of the story,” that guns had walked.

“We all think the best move” is to announce Wide Receiver “as part of Project Deliverance, where focus will be on aggregate seizures and not on particulars of any one indictment,” Weinstein wrote to Breuer in an April 28 email.

Less than a year later, Grassley asked then-acting ATF Director Ken Melson whether guns were being allowed to walk, prompting the broad denial from Weich.

Breuer said in his statement Monday that it was a “mistake” not to alert higher-ranking officials when the information about guns walking “became public,” given his knowledge about Wide Receiver.

“Knowing what I now know was a pattern of unacceptable and misguided tactics used by the ATF, I regret that I did not alert others within the leadership of the Department of Justice to the tactics used in Operation Wide Receiver when they first came to my attention,” Breuer said.

Breuer added that he had been assured that the weapons losses under Wide Receiver weren’t being repeated by Fast and Furious.

“When the allegations related to Operation Fast and Furious became public earlier this year, the leadership of ATF and the U.S. Attorney’s Office in Arizona repeatedly assured individuals in the Criminal Division and the leadership of the Department of Justice that those allegations were not true,” he said. “As a result, I did not draw a connection between the unacceptable tactics used by the ATF years earlier in Operation Wide Receiver and the allegations made about Operation Fast and Furious, and therefore did not, at that time, alert others within Department leadership of any similarities between the two. That was a mistake, and I regret not having done so.”

Neither Melson nor Dennis Burke, then the U.S. attorney for Arizona, are still serving in their positions. Melson was reassigned, and Burke resigned Aug. 30.