Mexican cartels are taking advantage of U.S. gun laws to buy thousands of weapons that are being used in an escalating drug war that has claimed more than 31,000 lives since late 2006, experts and law enforcement officials tell NBC News.
U.S. firearms agents estimate that around 80 percent of the weapons used by Mexican drug traffickers come from the United States, where cartel leaders are hiring Americans with clean records to make the purchases for them. In the past four years, Mexican authorities say they have seized 90,000 weapons from their nation's drug war.
"The cartels need their tools of the trade, which are the weapons, and they are coming to the U.S. to get those weapons," William McMahon of the Bureau of Alcohol, Tobacco, Firearms and Explosives told NBC News.
Authorities say the straw buyers are paid up to $200 per weapon and cite a recent case in Oklahoma City, where a former state narcotics agent pleaded guilty in such a gunrunning scheme.
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Francisco Reyes, 29, was accused of paying two friends to buy dozens of firearms destined for Mexico, according to court documents. One of those buyers, Jorge Alexis Blanco, bought at least 15 guns and attempted to buy three more, according to Michael Randall of the ATF in the criminal complaint.
"They are being taken advantage of by these cartels and really are providing something that's going be used to kill someone in Mexico," said McMahon, adding that the cartels are specifically looking for high-caliber weapons.
'Acapulco Police Massacre'
Authorities say they have no doubts that weapon purchases are being used to fuel the violence in Mexico, including a recent case known as the "Acapulco Police Massacre," in which four officers and three secretaries were murdered.
Guns used in that and other cases were traced to Houston. Overall, the Southwest border states, especially Texas, California and Arizona, are the primary sources of weapons used by the cartels in Mexico, where buying guns is much more difficult than in the U.S., according to the Department of Justice.Story: Mexico’s ‘war next door’ linked directly to United States
In 2009, ATF reported to Congress that about 90 percent of the guns recovered in Mexico that ATF has traced were initially sold in the United States. However, the National Rifle Association has said the percentage is much lower.
In smuggling weapons across the border, experts say, the guns are usually hidden in cars and trucks.
"They'll hide them in secret compartments, whether it's a spare tire, a gas tank, camper shells or they even build secret compartments to put them in there," said Rick Serrano, an ATF supervisor in Tucson, Ariz.
In Texas, authorities arrested Ernesto Gonzalez-Reyes, 48, in March alleging they found five 7.62mm semiautomatic rifles, 10 high-capacity 7.62mm magazines and 50 rounds of .40-caliber ammunition hidden within the cargo area panels and the front and rear bumpers of the Chevrolet Suburban he was driving.
'Not going to honest American hands'
During his visit to the United States in May, Mexican President Felipe Calderon urged a joint session of Congress to ban assault weapons that are showing up in his country.
Calderon said the U.S. need to "regulate the sale of these weapons in the right way."
"Many of these guns are not going to honest American hands," he said. "Instead, thousands are ending up in the hands of criminals."
Although U.S. officials say they have recently seized more than 10,000 weapons headed for Mexico, Mexican authorities say more work needs to be done to stem the flow, including better use of a gun-tracing program known as eTrace.
That program was announced in Mexico in January 2008 as the cornerstone of efforts to "terminate the illegal shipment of arms to Mexico and reduce the violence they cause on both sides of the border."
But a recent inspector general's preliminary report, first publicized in October, called eTrace underused and unsuccessful. One top official said not enough Mexican investigators had been trained or had access to the electronic database.
"It doesn't mean the system is not working. It's not working as well as it can," ATF Deputy Director Kenneth Melson told The Associated Press in October. "The information was being submitted by people who didn't know how to trace guns."
Melson said the system, when used properly, can provide strategic and intelligence information to fight gun-smuggling, establishing trafficking patterns as well as identifying weapons sources.
"We're now at a point where we can process much more information quickly, information that will be more accurate and more complete," Melson said.
But finding a way to stop the weapons flow, now known as the "Iron River," is being hindered to some extent by U.S. gun laws, officials say. In November, the inspector general of the Department of Justice detailed the problem, citing the lack of a federal statute specifically prohibiting firearms trafficking.
Meanwhile, Mexican authorities are taking steps to ensure the weapons that are seized don't find their way back to the cartels.
At a military base, in Mexico City, soldiers use torches and hammers to destroy thousands of guns, saving others for evidence in criminal investigations.
Mark Potter of NBC News and The Associated Press contributed to this report.