New evidence continues to arise, however, that Mexican crime groups, whose battles over drug routes and other criminal activities have claimed 40,000 lives since 2006, shop north of the Rio Grande for their firepower. Their favored firearms are variants of the AK-47 and AR-15 assault weapons, legally available at U.S. gun shops near the border.
In a video released earlier this month, a Mexican army defector who allegedly rose to become No. 3 in the brutal and powerful syndicate known as Los Zetas was asked by a police interrogator where Los Zetas obtain their weapons.
"From the United States," Jesus Rejon Aguilar, who was arrested by Mexican authorities on July 4, told his off-camera questioner. "All weapons come from the U.S."
Arturo Zamora Jimenez, a legislator from the once-ruling Institutional Revolutionary Party, made it clear in a telephone interview that he understands that many Americans firmly believe that their guns can protect against tyranny, and that they have the right to own and purchase them under the 2nd Amendment to the U.S. Constitution.
But he said lax U.S. gun laws are priming violence in Mexico.
"We know that the manufacture and sale of guns is a major economic activity for the people of the United States," he said. "But when these guns are used by rival organized crime groups abroad, the situation really changes because they are used in crimes that affect the lives and property of many people."
How much the Mexican government knew about the Fast and Furious operation remains unclear. Alejandro Poire, the top security spokesman for Mexican President Felipe Calderon, insisted last week that his government was not aware of the operation.
"If we had known about it, it would have been stopped," Poire told reporters.
But the federal Attorney General's office acknowledged that it had been informed of aspects of Fast and Furious.
"This gives you an idea of the lack of coordination within the Mexican government as well," said Javier Oliva, a national security expert at the National Autonomous University.
Opposition legislators are pressing for a further accounting of how much Calderon's government knew.
"It is lamentable that with the weapons brought into the country through this operation, there are thousands of dead Mexicans and the federal government can't give an explanation of its responsibility," said Dolores Padierna Luna, the secretary general of the leftist Democratic Revolutionary Party.
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