Updated

An official of the U.S. Bureau of Alcohol, Tobacco, Firearms and Explosives apologized Tuesday and told Congress he shares responsibility for mistakes in carrying out a controversial law enforcement operation in Arizona that resulted in high-powered weapons flowing into Mexico.

William McMahon, the head of ATF's Western region, testified Tuesday that the agency had good intentions when it launched Operation Fast and Furious in 2009. But McMahon said that looking back, there are things ATF would have done differently.

McMahon, the highest-ranking ATF official to testify publicly about the operation, said he failed to keep close enough track of the investigation in Arizona. Fast and Furious focused on several Phoenix area gun shops and sought to develop cases against gunrunning ring leaders who had eluded previous tactics.

Appearing before the House Oversight and Government Reform Committee, McMahon said he was committed to dismantling criminal networks on both sides of the border and that "in our zeal to do so, and in the heat of battle, mistakes were made. And for that I apologize."

Nationally, ATF has 4,600 open investigations under its Project Gunrunner which is designed to stop firearm trafficking into Mexico.

Fast and Furious is one of those investigations but it is the one trying new techniques to reach the previously untouchable leaders of gun-trafficking organizations.

ATF won't say how many agents are working on Fast and Furious for fear that disclosure would compromise the security of the operation. Overall 260 ATF agents are assigned to the entire U.S.-Mexican border area and participate in various Project Gunrunner probes.

Another ATF witness, William Newell, formerly in charge of the Phoenix field division, acknowledged that mistakes had been made "in how we handled" Operation Fast and Furious.

He said more frequent assessments of risky strategies like the one used in Fast and Furious would be "prudent."

Under questioning by both committee chairman Darrell Issa, R-Calif., and ranking Democrat Rep. Elijah Cummings of Maryland, Newell repeatedly said those running the operation did not intend that the guns would wind up in Mexico.

The goal of the operation was to let small-time gun buyers lead investigators up the chain to major illicit weapons traffickers along Arizona's border with Mexico. The strategy carried the risk that the tracking dimension of the program would be inadequate and that some guns would wind up in Mexico or on the U.S. side of the border in the hands of criminals and be used at crime scenes — which is what has happened. ATF intelligence specialist Lorren Leadmon testified that of more than 2,000 weapons linked to Fast and Furious, 227 were recovered in Mexico and 363 in the United States. The rest have not been recovered.