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When war broke out within the Sinaloa cartel, one of Mexico’s most powerful criminal organisations, people hoped it would last just a few months.
But more than a year and a half later it is still going, fuelled by a flow of firearms from the US – specifically from Arizona, which has surged past Texas to become the top source of guns seized in Mexico and traced to a recent US purchase.
“We have an enormous problem with gun trafficking by the Mexican drug cartels from Arizona down into Mexico,” Arizona’s attorney general, Kris Mayes, told the Guardian. “There is no doubt in my mind about that.”
When Mexican authorities recover guns, they can submit the serial numbers to be traced by their US counterparts. And according to the most recent available data, 62% of the guns seized in Mexico in 2024 and traced to a US purchase less than a year earlier – a key indicator they were bought to be trafficked – came from Arizona.
This coincides with the eruption of conflict in Sinaloa after Ismael “El Mayo” Zambada, who founded the Sinaloa cartel with Joaquín “El Chapo” Guzmán, was detained along with one of Guzmán’s sons after a small plane touched down in the US in July 2024.
Zambada accused Guzmán’s son of betrayal. Now a faction led by Zambada’s son is waging war against another led by the two sons of El Chapo who remain free in Mexico.
“We don’t know what their inventory of guns, ammunition, men and vehicles is,” said Miguel Calderón, coordinator of Sinaloa’s state council on public security, in December 2024. “I imagine they’re pulling together everything they have. This is the mother of all battles.”
Roughly 5,000 people are now dead or missing. And the factions show no signs of running out of guns.
Since the war broke out, Mexican security forces have seized almost 5,000 firearms in Sinaloa, which is roughly 20% of all the guns seized in the country in that time.
Mexico itself has strict gun laws and just two legal gun shops, where the weapons are sold by the Mexican military, meaning that its criminal groups look for their firepower abroad – and mostly in the US.
“The traced guns [from 2024] with a short ‘time to crime’ are very concentrated in the county where Phoenix is located,” said John Lindsay-Poland, coordinator of the Stop US Arms to Mexico project. “Others are coming from Tucson, and others from Texas. But the majority are now coming from Arizona.”
This is reflected in the fact that the Mexican state with the second highest number of gun seizures in 2025, after Sinaloa, is Sonora – which lies just over the border from Arizona.
“This is a change, because for many years, Tamaulipas on the Gulf coast was by far the state with most guns recovered,” said Lindsay-Poland. “And Texas was also dominant in the number of guns sold and then found in Mexico with a short time to crime.”
Like Texas, Arizona is a state where it is relatively easy to buy a firearm. Cartel associates often recruit Americans to be “straw purchasers”, sending them into stores to buy them guns in return for a commission, before those guns are trafficked south over the border.
Mayes, the attorney general, recently announced the indictment of one gun-trafficking ring involving 20 people that bought more than 330 firearms, many of which ended up in Mexico, but she suspects “this is just the tip of the iceberg”.
According to Mayes’ office, the markup for trafficked guns – and especially rifles such as the AR-15 and the AK-47 – has spiked in Mexico, feeding through into higher commissions for straw purchasers in Arizona, possibly reflecting demand driven by cartel infighting.
The Mexican government has an ongoing lawsuit against five Arizona gun shops it has accused of facilitating gun trafficking, while Claudia Sheinbaum, Mexico’s president, has also called on Donald Trump to help stem the flow of illegal firearms to Mexico.
But for now the border between Arizona and Sonora – which is also where most seizures of fentanyl coming into the US take place – is a focal point for trafficking.
“Arizona is the fentanyl funnel for the rest of the [US], and it’s also where firearms are being funnelled down into Mexico,” said Mayes. “So this is a twin problem.”
