Images of charred, bullet-ridden trucks on a remote highway in Sonora and an hourslong gunbattle in the heart of Culiacan, Sinaloa, horrified the U.S. public in recent weeks.

The images showed where the “iron river” of guns and ammunition bought in the United States empties onto the streets of Mexico.

The headwaters of that river often spring from Southern Arizona, where federal court records show young people buying weapons for $100 payouts, a man buying rifles from gun stores every few days for nearly a year in Green Valley and Tucson, and heroin addicts selling .50-caliber rifles to their dealers.

After the fatal shooting of three women and six children in La Mora, Sonora, on Nov. 4, Mexican officials announced that some of the ammunition used in the attack came from the U.S.

To get a closer look at how the iron river flows from Southern Arizona into Mexico, the Arizona Daily Star analyzed the 32 weapons-smuggling cases involving Mexico filed in federal courts in Tucson and Phoenix in 2018.

Read more: Arizona guns quietly smuggled across border as bullets fly in Mexico

The cases show that rather than dam up the iron river midstream at the Arizona-Sonora border, federal agencies focus on where the river ends and where it begins.

Only a handful of prosecutions came from firearms and ammunition being smuggled into Mexico through Arizona’s ports of entry. Most cases came from federal agents scouring suspicious paperwork at gun stores in Tucson and Phoenix or following up on firearms recovered in Mexico that were traced back to Arizona.

At Arizona’s ports of entry, customs officers catch thousands of pounds of hard drugs every year and inspect millions of travelers heading north, but they only caught six rifles and four handguns heading south in fiscal 2019, according to data provided by U.S. Customs and Border Protection. Since 2012, customs officers in Arizona caught 106 rifles, 88 handguns and 202,000 rounds of ammunition.

Far more weapons were caught in Sonora after they crossed the border. Since 2009, the Mexican military recovered 6,700 illicit firearms, including 4,200 rifles, the Mexican newspaper El Imparcial reported on Nov. 18.

Firearms are largely illegal for civilians in Mexico, but they are used widely by drug cartels and other criminal groups.

The Mexican military estimates 1.6 million illicit firearms are circulating in Mexico, the Milenio news outlet reported in August. The estimate included 200,000 firearms smuggled into Mexico each year, most of which came from the U.S. but also from Spain, Italy and Austria.

A more solid number comes from weapons traced back to the U.S. after Mexican authorities recover them at crime scenes, find them abandoned, or under other circumstances. More than 67,000 firearms recovered in Mexico were traced to the U.S. from 2013 to 2018, according to ATF data.

The narratives included in court cases and search-warrant affidavits illustrate what Mexican commentators call an “operación hormiga,” or “ant operation,” of quietly buying firearms in Southern Arizona and smuggling them in small numbers across the border.

Even one such purchase can have “devastating repercussions” in Mexico, Angela Woolridge, a federal prosecutor who handles many of the firearm cases in Tucson’s federal court, wrote in sentencing memorandums.

“It is impossible to know how many people already have been or will be threatened, injured, or killed because of the single firearm the defendant purchased,” Woolridge wrote.

Last weekend, three people were fatally shot in San Luis Rio Colorado, the Mexican border town south of San Luis, Arizona. Mexican authorities recovered high-powered rifles, tactical gear and a rocket-propelled grenade launcher.

Grenade launchers were at the heart of a 2018 case in which an undercover Homeland Security Investigations agent set up two sting operations in Tucson and Chandler.

A man who was not named in court documents contacted the HSI agent online and asked about buying an M-16 automatic rifle and a grenade launcher. He and the undercover agent set a price of $3,650 and met in the parking lot of a big-box store in Tucson in September 2018. The man was arrested, as were two men the following month who met with the agent in Chandler to buy three machine guns with attached grenade launchers for $10,500.

Another highly destructive weapon that figures prominently in cartel violence is the .50-caliber rifle, which can pierce armor and bring down helicopters.

When Mexican soldiers in Sinaloa took into custody the son of Joaquin “El Chapo” Guzman Loera, the former leader of the Sinaloa Cartel, on Oct. 17 they set off an hourslong gunbattle with cartel soldiers, some of whom used .50-caliber rifles.

The .50-caliber rifles are “what the cartels need to strengthen their particular ‘armies,’ if you will,” said Monique Villegas, special agent in charge of the Phoenix office of the Bureau of Alcohol, Tobacco, Firearms, and Explosives. If a competing cartel gets .50-caliber rifles, “that’s what they’re going to start looking for in the U.S.”

Buying one is relatively easy in Arizona and elsewhere, Villegas said.

“My 86-year-old grandmother could walk into a store and buy a .50-caliber rifle if she wants to,” Villegas said.

Michael Huynh, 29, and Katie O’Brien, 28, both Tucsonans, did just that on several occasions, court records show.

They were sentenced in September to five years in prison after they bought three .50-caliber rifles on behalf of their heroin dealer, who would then arrange to have them smuggled into Mexico. One of the .50-caliber rifles, a belt-fed TNW HBM2, is so heavy-duty that it is mounted on a tripod.

Huynh later said he had bought about 50 firearms for his heroin dealer in the previous year.

A rifle that Huynh bought in October 2017, a Century Arms RAS47 assault rifle, was recovered in Mexico three months later after a shootout between Mexican law enforcement and a cartel in La Paz, Baja California Sur.

During their investigation, ATF agents learned that another man, who was not charged, bought a Colt M4 rifle for Huynh’s heroin dealer in March 2017. That rifle was recovered in Culiacan four months later.

Although port busts are relatively rare, when they do happen they can lead to complex investigations.

In November 2017, customs officers busted a vehicle containing six firearms at a port of entry in Nogales, Arizona. Investigators found that one of the firearms was sold online to Gardenia Rincon Avilez two days before the bust, court records show.

Five months later, police in El Mirage searched the home of Nicholas Brasseur, a licensed firearms dealer, and found paperwork showing he had sold 50 lower receivers for AR-15 type rifles to Rincon in March 2018 for $21,000 and another 53 receivers to an associate of Rincon.

Brasseur told agents that Rincon had said she planned to take the receivers to Tucson, where they would be converted to fully automatic rifles and then taken to Mexico.

Weeks later, customs officers in Nogales stopped Rincon as she drove into Arizona. She told agents that she bought the receivers and took them to her sister’s house in Scottsdale, where she stored them in a Tupperware box in the garage.

She eventually took them to Tucson and sold them to the man who had told her which weapons to buy. She sold them for $700 each, or a profit of about $400 per receiver, according to court records.

Rincon said she was given cash in Mexico and brought it to Arizona to buy weapons. On one occasion, she was asked to buy a FN M249 belt-fed rifle in Phoenix. She bought the rifle for $8,000 and sold it in Tucson for $12,500.

Two of the rifles she bought in March 2018 were later recovered in Mexico.

Young buyers

In June 2017, an otherwise law-abiding 18-year-old in Tucson was pressured by a family friend to buy a rifle. The friend gave him the money and told him to buy a Century Arms WASR-10 assault rifle from a gun store in Tucson.

In exchange for $100, the young man lied to the store employee and said the rifle was for his own use, making him one of a half-dozen “straw buyers” in a smuggling ring that moved rifles through Nogales into Mexico, including one recovered in Culiacan, Sinaloa.

In another case, a 23-year-old woman bought a Century Arms RAS47 pistol in Tucson at the request of her boyfriend in December 2017. Hours later, he smuggled it through Nogales into Mexico. The pistol was used in a crime in Sinaloa less than two months later.

Young buyers are common in Arizona and throughout the states bordering Mexico, said the ATF’s Villegas.

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“They probably have no ties to the cartel,” Villegas said, and instead are just looking to make a “quick couple hundred dollars.”

“A lot of these people don’t know guns really,” Villegas said. “They are told which guns are needed at that time and told which ones to get.”

Straw buyers need to have clean criminal histories and “the chances of having a criminal record goes down if you’re young,” said Scott Brown, special agent in charge of Homeland Security Investigations in Phoenix.

As is the case with various types of crime, “some young people don’t recognize the significance of their actions,” Brown said.

Young people acting as straw buyers are among the biggest challenges to shutting down cross-border firearms trafficking in Southern Arizona, he said.

He called it “troubling” that so many people would agree to be straw buyers without “recognizing that you are buying a gun that is intended to be used in a crime by people with a callous attitude towards life,” Brown said.

Repeat buys

Gun-trafficking rings buy the same type of weapon over and over, court records show.

“Cartels know they can go to multiple stores and buy one or two firearms and it won’t pop up as a trafficking scheme,” Villegas said.

In one of the most egregious cases the Star found, Alejandro Navarro Mendez pleaded guilty earlier this month to buying 108 firearms knowing they would be smuggled into Mexico. His most common purchases were Savage .22-caliber rifles, which accounted for 36 of the firearms he bought.

He started buying the firearms in October 2017 and by the following February he had found his rhythm.

On Feb. 3, 2018, he walked into a sporting goods store in Tucson and bought a Ruger SR22 .22-caliber pistol. Three days later he bought three Savage 62F .22-caliber rifles at a Walmart in Tucson. On Feb. 9, he bought an Umarex Beretta 92 .22-caliber rifle at the same sporting goods store that he went to before.

On Feb. 12, he bought a Savage 64F .22-caliber rifle at a second Walmart in Tucson. Five days later, he bought a Glock 42 .380-caliber pistol from a small gun store in Tucson. The next day, he went back to a Walmart and bought a Savage 64F .22-caliber rifle. On Feb. 24, he went back to the small Tucson gun store and bought a Kel-Tec PMR30 .22-caliber pistol.

Every few days until September 2018, he cycled through different stores in Tucson and Green Valley, including 45 visits to four Walmart stores.

The road ahead

After the shooting in La Mora, Brown expects more national-level enforcement initiatives will start appearing. Villegas pointed to recent announcements by the Department of Justice of a crackdown on gun violence in the U.S.

At the federal courts in Tucson and Phoenix, prosecutors still lack a law specific to cross-border smuggling of firearms.

Instead, they generally charge gun smugglers at ports of entry with trying to export goods without a license.

Those accused of making straw purchases are charged with making false statements on ATF forms. Individuals who sell numerous guns can be charged with operating a firearms business without a license.

The number of these prosecutions continues to lag behind cases related to other border-related crimes. While 32 cases of smuggling firearms into Mexico were brought in federal court in Tucson and Phoenix in 2018, prosecutors filed 750 drug-smuggling cases that year and thousands of border-crossing cases.

The billions of dollars that can be made by selling drugs in the U.S. “cartels are going to continue to fight to sell drugs and make money,” Villegas said.

“As long as the need for drugs is there, guns will be going south,” she said.

Contact reporter Curt Prendergast at 573-4224 or cprendergast@tucson.com or on Twitter @CurtTucsonStar