An ornate Colt .38 Super pistol – considered a status weapon in Mexico – for sale at Mo Money pawnshop in Phoenix

There was a national ban on assault weapons that lapsed in 2004. Obama has not tried to revive it, nor has Congress moved to renew it despite repeated pleas by Calderón’s government to do so. Critics of the ban, including some people in law enforcement, point out that it was mostly about style anyway: An AK-47 or AR-15-type rifle could be “sporterized” by manufacturers with a few tweaks – such as changes to the stock and muzzle – and be just as lethal but perfectly legal. When the ban lapsed, some states passed their own laws restricting the sale of assault weapons, but not Arizona.

Under Republican Governor Jan Brewer this year, the Arizona Legislature has removed permit requirements for concealed weapons, blocked cities from restricting guns in city parks and preserves, and exempted Arizona firearms manufacturers from all federal regulations if the guns are sold in-state – a move aimed at a state’s rights court challenge against federal authority. The state Legislature has rejected attempts to close Arizona’s so-called “gun show loophole” and this year rejected an effort to create a state crime for straw purchases of firearms – a measure backed by Democratic Arizona Attorney General Terry Goddard, whose office prosecutes some gun-trafficking cases. When Brewer spoke at the National Rifle Association’s annual convention in Phoenix last year, she said better border security, not new gun laws that restrict the rights of law-abiding Americans, is needed in response to violence in Mexico. (The governor’s office did not return repeated phone calls or e-mails seeking comment for this story.)

The NRA, which also did not return calls for comment, insists that existing regulations are sufficient. A statement on the website for the NRA Institute for Legislative Action says: “The United States has very strong criminal laws that apply to every link in the trafficking chain, between the first acquisition of a firearm in the U.S. and its transportation to Mexico or any other country. Strong enforcement of existing U.S. firearm laws, and cooperative enforcement programs with Mexican authorities, are likely to be more productive than added restrictions on firearm transactions by U.S. citizens.”

But Holmes, of the Arizona Attorney General’s Office and the Southwest Border Anti-Money Laundering Alliance, says he believes the lack of regulations on firearms in Arizona seems unreasonable to many Mexicans. “They look at us and they see people who could keep them from being murdered by keeping guns out of the hands of their potential murderers,” he explains. “They know we have the Second Amendment… but they see things we could do, actions we could take that we are not taking.”

Holmes says he believes one of the things the U.S. could do would be to restrict the sale of certain types of military-grade weapons with limited sporting use, such as semi-automatic .50-caliber rifles. (Fully automatic machine guns and grenade launchers are legal to own in Arizona but are subject to strict federal registration requirements and other regulations.)

Dennis K. Burke, U.S. Attorney for the District of Arizona, says an “iron river” of weapons flows from Phoenix to Mexico.

In the United States, .50-caliber rifles have seldom if ever been associated with criminal uses and are used recreationally for long-range target shooting. But the ATF says it has seen an increase in trafficking of .50-caliber rifles to Mexico to be used in assassinations. These huge weapons can be mounted on vehicles or used for sniper attacks. Some versions of the gun, including some the ATF confiscated in Yuma en route to Mexico earlier this year, are more than 5 feet long and weigh more than 50 pounds. The cartridges are more than 5 inches long and cost about $5 each. With a day’s training people can hit a target the size of a dinner plate from a mile away, Newell says. He forms a circle around his face with his hands. “What’s the size of a plate?”

In 2008, the ATF busted a man in Phoenix who specialized in getting .50-caliber rifles for the cartels. Weapons linked to Victor Varela, an electrician, included several .50-caliber rifles and were seized in Juarez after a deadly shootout with Mexican authorities. The ATF used an informant to nab Varela buying more .50-caliber weapons in Phoenix. There are no federal or state statutes specific to gun trafficking. So while gun trafficking can be a sentencing enhancement, it is not a crime someone can actually be charged with. At the federal level traffickers are usually charged with lying on the federal background check form. Varela was prosecuted by the Arizona Attorney General’s office and charged with forgery and fraud. He was sentenced to two and a half years in prison.

A month after Munoz and Gutierrez went on their buying spree, an ATF agent reviewing multiple handgun sales reports recognized Munoz’s name from tips from informants, Forcelli says. The agent ran a background check and discovered Munoz’s felony conviction, which makes it illegal for him to buy firearms. Since there is no federal database of gun purchases, agents began going store to store in Phoenix and Yuma with Munoz’s picture. They learned he had been asking about acquiring some fully automatic machine guns. Since illegally buying machine guns would be a better case, the ATF laid a trap. An undercover agent distributed fake business cards at gun stores along with a story: You call the guy on this card because he can get you anything. (Several other people called the agent inquiring about the weapons, Forcelli notes grimly.)

On August 28, 2009, more than eight months after the handgun purchases that first flagged the ATF, Munoz brokered a deal to buy machine guns. Court records show he offered a cousin, a former co-worker, the co-worker’s brother and Gutierrez $1,000 each to come along with him for protection. Gutierrez drove them to Phoenix in his white Kia minivan with a .50-caliber, semi-automatic, belt-fed rifle in the back. They delivered the weapon to two men in a Phoenix motel room who authorities suspect may have been affiliated with Mexico’s Sinaloa drug cartel.

Munoz and his team then drove to a storage locker in Maryvale where Munoz had arranged to purchase the machine guns from the undercover officer. He paid $15,000 cash for eight fully automatic AK-47 rifles and a Colt M16A1 machine gun with an attached grenade launcher. As the men loaded the machine guns into the van, ATF agents surrounded them.

In the spring, the men all pled guilty to federal firearms charges. As the ringleader, Munoz was sentenced to 10 years in prison. In court, wearing an orange prison uniform and shackles, Munoz told the judge he made “bad decisions” and accepted responsibility for what he had done. (Forcelli says he refused to cooperate with investigators or give them information on anyone else he was working with – a common problem because people are afraid the cartels will take revenge on their families.)

At Munoz’s sentencing hearing, assistant U.S. Attorney Emory T. Hurley, the office’s senior adviser on gun trafficking, explained that the guns were trafficked to Mexico and had not yet been recovered. “The fact that firearms leave the country doesn’t mean their damage to humanity is any less severe,” he said.

After handing down Munoz’s sentence, U.S. District Court Judge James A. Teilborg said Munoz’s smuggling “looks like an effort to start a war, and war may be the ultimate result.

“The seriousness of this cannot be overemphasized,” he said. “The loss of human life is not hard to imagine, or difficult to trace.”