Three agents from the Bureau of Alcohol Tobacco and Firearms marched to Congress on Wednesday to blow the whistle on a risky operation targeting gun traffickers.

They told the House Government Reform Committee that more than 1,000 guns tied to the ATF’s investigation of drug cartels are still missing somewhere in the U.S. and Mexico. Lawmakers want to know who approved the operation in the first place.

The ATF agents testified that they tried for months to sound alarms about an operation called Fast and Furious, where federal officers in Arizona watched AK-47s being sold to people who’d pass them illegally to Mexican cartels.

The whistleblowers say they wanted to intervene early and arrest the so-called straw buyers. But time after time, higher ups who wanted to build big criminal cases against drug kingpins directed them not to act, they said.

ATF agent Peter Forcelli didn’t mince words.

“Sir, it’s my belief that what we have here is actually a colossal failure in leadership from within ATF, within the chain of command involved in this case, within the United States Attorney’s office and within DOJ as to the individuals who were aware of this strategy,” Forcelli told lawmakers.

Forcelli told Congress he never understood the strategy behind the ATF operation. To watch guns walk across the Southwest border, he said, was a recipe for disaster.

“We weren’t giving guns to people who were hunting bear. We were giving guns to people who were killing other humans,” he said.

Two assault weapons purchased by a straw buyer who was targeted by investigators were recovered last December near where U.S. border patrol agent Brian Terry died in a firefight with Mexican bandits. Federal sources say they don’t think the guns were used to shoot Terry, but they were found at the scene of his death.

Terry’s cousin, Robert Heyer, spoke for the family at Wednesday’s hearing.

“Brian did ultimately come home that Christmas. We buried him not far from the house that he was raised in, just prior to Christmas Day,” Heyer said.

ATF whistleblower Olindo Casa said there are more than 1,000 weapons from Fast and Furious still on the loose.

“Anytime there’s a shooting in the general Phoenix area or even in Arizona, we’re fearful that it might be one of these firearms,” Casa said.

Congressional investigators released emails from a government strategy meeting in 2009 when senior officials from the Justice Department, the ATF and the FBI agreed to focus on bigger cases against the networks that traffic guns to Mexico.

California Republican Rep. Darrell Issa has been pressing to find out who in Washington knew about the operation.

“We want to know what felony stupid bad judgment led to allowing this program at the highest level,” Issa said at the hearing.

Prosecutors and congressional Democrats have said weak gun laws contribute to the violence on the Southwest border. But there’s little political will in Congress to open up the divisive issue.

Ron Weich, speaking for the Justice Department, told lawmakers the federal policy on guns crossing the border is clear.

“The Attorney General has made very clear that guns cannot walk to Mexico, that is to say it is a violation of law for guns to be transported across the border to Mexico,” Weich said.

Issa has promised to hold more hearings to get to the bottom of the scandal.

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