A gunsmith from a rural town, a former Marine, and half a dozen others were under investigation in San Antonio, Texas, starting in the summer of 2018 for trafficking more than half a million dollars worth of guns and ammunition to the Cartel del Noreste, a drug cartel prominent in northeast Mexico with connections to former Mexican soldiers.

Jose J. Soto Jr. was in the U.S. Armed Forces from 2004 to 2015, including a stint with the elite Army Rangers. He came on Homeland Security Investigations’ radar around 2017 for working with a human trafficker and gunrunner for the cartel.

Through 2018, Soto and gunsmith Brian Morris purchased hundreds of rifles, including .50-caliber Barretts. Morris often purchased the rifles or their parts, built them out into unserialized “ghost” machine guns and sold them to Soto. Soto flipped the weapons to Cartel del Noreste, also commonly referred to as the Northeast cartel.

The gun dealer Zeroed In Armory sold more than 170 firearms to Morris over eight months. Two were later recovered at Mexican crime scenes. A federal agent reviewed invoices totaling US$122,225 in weapons sales to Morris, but Zeroed In continued business unencumbered.

And Zeroed In wasn’t the traffickers’ biggest supplier. CDNN Sports Inc., a firearm dealer currently based out of Abilene in central Texas, sold $280,000 worth of magazines, high-powered ammunition and assault rifles to Soto. Soto flipped the weapons to the cartel.

Independent firearm businesses like Zeroed In Armory are the largest suppliers of crime guns bought in the U.S. and trafficked to Mexico.

We are a professor of economic development and an investigative journalist. We have spent a year sifting through documents and datasets during our investigation of gun trafficking to Mexico and its effects. We built a dataset of trafficked weapons linked to 100 U.S. court cases. We combined this with leaked records of crime guns that were seized by authorities in Mexico from 2018 to 2020 and traced back to gun dealers in the U.S. by the ATF.

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

In this combined dataset, independent gun dealers accounted for 83% of weapons trafficked to Mexico that we can trace back to U.S. dealers, including most of the most dangerous types of trafficked guns. Chain stores sold the other 17%.

We also found that the most dangerous types of trafficked guns originated predominantly from independent stores. Fifty-caliber sniper rifles were 60 times as likely to come from independent dealerships compared to chain stores, and 7.62 mm assault-style weapons are 16 times as likely to do so.

Zeroed in Armory tops the list of independent gun dealers, with 488 crime guns from Mexico traced back to the store. But CDNN Sports doesn’t appear on the list despite the sales to traffickers because the individual guns they sold Soto were not found in the public documents for his case. Most weapons that are trafficked aren’t seized or traced back to dealers, and those that are are largely obscured from public view.

Second on the list is Pete’s Sport Shop in Madera, California, where traffickers bought over 400 Ruger rifles between October 2007 and March 2009, often dozens at a time. One defendant said he recruited people for........

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