NOGALES, Ariz. — Gun runners once were so nonchalant about driving into Mexico that one smuggler stashed a .50-caliber rifle on the top of the engine block of a sedan, the weapon visible to anyone who bothered to pop the hood.
It was 2010 and word hadn't yet spread that U.S. officials were beefing up outbound inspections, searching for guns that were fueling Mexico's raging drug war. Border agents confiscated the rifle and hundreds of other weapons and ammunition during the first few years of stepped-up enforcement along the southwestern border, federal data show.
Mexican officials have also taken action, installing scales to see whether southbound cars are abnormally overweight — a possible indication of gun smuggling.
But as inspections have become more aggressive, smugglers have become more sophisticated.
Instead of sending a big shipment of AK-47s in one vehicle, U.S. officials said, arms traffickers dismantle weapons and transport the pieces in separate vehicles. A bolt carrier here. A flash hider there.
Smugglers have also used drivers who theoretically would avoid suspicion. Agents once recovered ammunition in the molding of a minivan. The vehicle was driven by a father. Mom sat beside him, with kids in the back.
In December, one smuggler trying to pass through the San Luis port of entry in western Arizona concealed ammunition magazines in the rear seat, door panels and rear bumper of a 1991 Oldsmobile Cutlass.
Jose Angel Palacios pleaded guilty in May to smuggling 60 magazines that could be used with AK-47s, a weapon of choice for drug cartel enforcers. Palacios, 20, a Mexican national, told authorities he had been promised $150 to make the delivery.
At least 2 of every 3 firearms confiscated in Mexico from 2007 to 2011 were purchased in the United States and smuggled south, according to the Bureau of Alcohol, Tobacco, Firearms and Explosives. Many of the weapons ended up in the hands of criminal organizations and were used against the military, journalists and civilians.
"In the last six years, they had over 70,000 people murdered in drug-related violence, and a vast majority were using very sophisticated firearms that came from the United States," said Eric Olson, associate director of the Latin American Program at the Woodrow Wilson International Center in Washington. "It's having a dramatic impact on Mexico."
Experts and scholars say the problem is due largely to laws that make it difficult to prosecute gun trafficking, especially by straw buyers — people who can pass background checks and purchase guns only to turn them over to drug cartels.
"I think the 2nd Amendment is being scapegoated for a problem that is rooted in Mexico," said Andrew Arulanandam, spokesman for the NRA Institute for Legislative Action. "There is pervasive corruption within the ranks of government, military, law enforcement and judiciary. That's the root of the problem."
Mexican officials did not provide comment on the issue despite repeated inquires.
The NRA took issue with the ATF data on gun smuggling, describing the agency's findings as incomplete because they relied on Mexican officials, who the NRA says are likely to report guns only from the U.S.
"You are talking about multimillion-dollar criminal enterprises that have sophisticated armored cars," Arulanandam said. "The very premise that these drug cartels are buying their firearms one firearm at a time from a gun show in Arizona or Texas is ludicrous."
Still, that is what's happening, contended Olson, who leads a group of researchers who study gun trafficking.
In a report, Olson's group argued that prosecuting gun trafficking is difficult because of weak or imprecise laws. Straw purchasing is not a felony under federal law. If convicted, a straw purchaser may simply have to pay a fine of a few hundred dollars for what amounts to lying on a form.
In Arizona, going after straw buyers has proved frustrating, said former Arizona Atty. Gen. Terry Goddard.
He recalls how state prosecutors in 2008 accused the owner of X Caliber Guns, a gun shop in a Phoenix suburb, of arming Mexican cartels. A judge dismissed the case, stating there wasn't enough proof, based on the state law's limited definition of straw purchasing.