A botched federal program that funneled more than a thousand firearms to Mexican drug lords became the target of bipartisan denunciations at a Congressional hearing on Tuesday.

A highly critical report released on Tuesday detailed serious oversights in Operation Fast and Furious, a program jointly spearheaded by the Department of Alcohol Tobacco and Firearms and the U.S. Justice Department that employed a technique, known as "gunwalking," in which agents deliberately do not halt illegal gun purchases, instead seeking to trace them to their source. But the agencies failed to communicate with each other or with Mexican authorities, and weapons later resurfaced at crime scenes.

"It's incomprehensible that officials at the Justice Department, the ATF and the U.S. attorney's office would keep their counterparts at the U.S. embassy in Mexico City in the dark about Operation Fast and Furious," U.S. Sen. Chuck Grassley, R-Iowa, said in a press release. "Keeping key details secret while straw purchasers continued buying weapons for gun traffickers jeopardized our relationship with our southern ally and put lives at risk."

Officials from the ATF apologized for the program but sought to defend it in testimony before Congress, contradicting lower-level agents who alternately described the program as "insane,"  a "disaster" and a "perfect storm of idiocy, while charging that their warnings to higher-ups were rebuffed or ignored. The differing accounts drew an angry reaction from Rep. Darrell Issa, R-Calif., when William Newell, former special agent in charge of the Phoenix field office, denied that they allowed guns to "walk" across the border.

"Are [the other agents] lying, or are you lying?" Issa asked Newell.

In 2009, ATF agents in Mexico noticed a sharp rise in the number of guns appearing at crime scenes. Carlos Canino, an ATF agent stationed in Mexico, expressed alarm to his superiors after linking guns at the scene of a bloody shootout between the Sinoloa cartel and the La Familia cartel to the United States. But in a pattern that recurred throughout, he remained ignorant of the operation's scope and was reassured that it was a success. Canino's boss described regular "screaming matches" with their superiors.

"I can say with authority 'walking guns' is not a recognized investigative technique," Canino testified. "These guns went to ruthless criminals. ... It infuriates me that people, including my law enforcement, diplomatic and military colleagues, may be killed or injured with these weapons."