Illegal firearm trafficking is inseparable from the illegal drug trade: Weapons are often bought with drug money, can strengthen cartels and can be traded for drugs.

In the spring of 2021, the Bureau of Alcohol, Tobacco, Firearms and Explosives, known as ATF, started a gun-trafficking investigation that ran from Idaho, down through California and into Mexico. The investigation uncovered a scheme to drive pounds of narcotics north, and some of their “white China” and black tar heroin were exchanged for guns that an Idaho Falls resident purchased out of a firearm seller’s garage.

By the summer, ATF and other federal agents tracked the traffickers to a hotel off West Broadway Street in downtown Idaho Falls, where they observed a suspected drug deal and apprehended their suspects.

Their final haul included 15 pounds of meth, a pound of heroin, 3,000 fentanyl pills and 16 handguns and rifles.

The trafficking web

The incident fits into a larger web of trafficking guns south to Mexico and narcotics north to the American Midwest and coasts. The Louisville Courier Journal documented the connection in their investigation into cartel drugs poisoning Oregon.

We are a professor of economic development and an investigative journalist, and we have spent a year sifting through documents to follow the flow of illicit weapons trafficked from the U.S. to Mexico.

This trafficking web regularly shows up in prosecutions, including 14 federal sentences in North Carolina that included dozens of firearms and hundreds of pounds of narcotics.

Our collection of court records and gun data traces the relationship throughout the United States.

Read the full investigation: Mexican drug cartels use hundreds of thousands of guns bought from licensed US gun shops – fueling violence in Mexico, drugs in the US and migration at the border

Of the 100 court cases we cataloged, nearly one-fifth explicitly mention drug trafficking in connection to the confiscated firearms.

Drugs for guns

In 2020, Pedro Roberto Hernandez-Gomez was caught in Los Angeles attempting to exchange a kilogram of fentanyl and a kilogram of heroin for three machine guns and three grenade launchers.

And in March 2024, Xavier Drew, also known as “Flock,” was sentenced to 13½ years in prison for selling several pounds of meth, fentanyl and nearly a dozen firearms to undercover agents. The guns included a semiautomatic pistol and pistols with obliterated or missing serial numbers. He also sold them Glock switches, or machine-gun conversion kits. A collaborator, Esvin Ivan Calles-Corrales, was sentenced to five years for shipping narcotics and facilitating the transfer of related proceeds to Mexico.

Closer to the border, in August 2022, Maria Del Rosario Navarro-Sanchez, aka Fernanda, coordinated gun purchases in the U.S. – using drug funds from Mexico for the Jalisco Nueva Generación cartel and courier deliveries of meth and fentanyl pills from Mexico through El Paso, Texas – with Brian Munoz-Castro.

Munoz-Castro distributed the narcotics to separate couriers, who delivered the drugs throughout the U.S. Federal agents arrested Munoz-Castro in a gun store parking lot in March 2023 after he picked up gun parts from an El Paso gun shop. He later took the agents to his home in El Paso where he had close to 2½ kilos of meth.

Federal agents indicted Navarro-Sanchez after they intercepted her communications with former Juarez, Mexico, city hall police officer Rene Hernandez-Cordero.

The agents tracked a gun exchange involving Hernandez-Cordero at a Circle K in El Paso. Twenty assault rifles and two Barrett .50-caliber rifles were set to be trafficked into Mexico in August 2023 in the back of a pickup truck for the purchase price of US$66,000.

When Munoz-Castro was convicted in September 2024, Navarro-Sanchez was still a fugitive, according to the U.S. attorney’s office. Munoz-Castro received a 10-year sentence for his role.

At the hearing, the defense tried to call out the absurdity of so many weapons just thrown into the back of a pickup truck and driven across the border. “That’s inherently ridiculous, isn’t it?” the attorney asked.

Mark Cervantes, a U.S. Customs and Border Protection enforcement officer, answered by pointing to the ubiquity of these kinds of trafficking actions. “I’ve had one instance where an individual had 20 SCAR assault rifles and 30 Glock pistols without concealment in the vehicle,” he said.

With some 135,000 firearms traveling across the border annually, it’s not a surprise that some traffickers might be so brazen.

Read the full investigation: Mexican drug cartels use hundreds of thousands of guns bought from licensed US gun shops – fueling violence in Mexico, drugs in the US and migration at the border

The authors do not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and have disclosed no relevant affiliations beyond their academic appointment.