WASHINGTON — Three federal gun agents told a House committee Wednesday that dozens of gun traffickers suspected of working for Mexican drug cartels were "allowed to walk free" during an investigative operation that allowed hundreds of guns to fall into the hands of cartel enforcers and other criminals along the southwest border.

In emotional testimony before the Committee on Oversight and Government Reform, the Phoenix-based Bureau of Alcohol, Tobacco, Firearms and Explosives agents also apologized to the family of U.S. Border Patrol agent Brian Terry, slain last year by alleged cartel associates in a firefight where two weapons purchased in the risky ATF program were recovered.

"What we have here is a colossal failure of leadership," said ATF agent Pete Forcelli, a supervisor in the Phoenix office. "We weren't giving guns to people for killing bear, we were giving guns to people to kill other humans. This was a catastrophic disaster."