Mexico Demands Answers After Investigation Links U.S. Military Ammunition to Cartel Massacres
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— Key Points This is part of The Rio Times’ daily coverage of Mexico affairs and Latin American financial news.
Mexican President Claudia Sheinbaum on Monday called it a matter of serious importance: a new investigation revealing that drug cartels operating across her country have been using ammunition manufactured for the United States Armed Forces.
Speaking at her daily press conference, Sheinbaum said her government would first verify the report and then engage Washington directly.
“We are reviewing the report to be able to speak with the U.S. government about this issue and see how it is possible that these weapons, which are for the exclusive use of the U.S. Army, are entering Mexico,” she said.
The report in question, published Saturday by The New York Times and the International Consortium of Investigative Journalists, traces the path of .50-caliber ammunition from the Lake City Army Ammunition Plant — a sprawling, government-owned facility outside Kansas City, Missouri, operated by defense contractor Olin Winchester — into the hands of Mexican criminal organizations.
Built on millions of pages of court documents, seizure records, and government data, the investigation reveals how agreements between the Army and private contractors have allowed military-grade rounds designed to destroy vehicles and bring down light aircraft to flow into civilian retail markets. From there, the ammunition has been purchased in bulk — often from online retailers — and smuggled across the border.
The numbers are stark. Since 2012, the Bureau of Alcohol, Tobacco, Firearms and Explosives has seized more than 40,000 rounds of .50-caliber ammunition in U.S. states bordering Mexico. About a third were traced back to Lake City — more than from any other single manufacturer.
At least 16 online retailers sold armor-piercing variants of the round. One seller told investigators he stopped only after realizing where his product was ending up: buyers were ordering 100-round ammunition cans shipped to residential addresses.
The strategic significance of these rounds is not about quantity — it is about what they can do. Former ATF agent Chris Demlein, who spent years investigating gun smuggling to Mexico, told ICIJ that .50-caliber ammunition has been a game changer for the cartels.
“The impact that one .50-cal has in a firefight is outrageous,” he said. “They really tip the scale.” Investigators found Lake City casings at the scene of a 2019 cartel assault on the town of Villa Unión, in Coahuila, where more than a hundred gunmen attacked a police station for over an hour with heavy machine guns.
In early 2024, gunmen used Lake City armor-piercing incendiary rounds to attack a police convoy, penetrating an armored vehicle and killing one officer. Mexico’s then-Defense Secretary, Luis Cresencio Sandoval, admitted that his forces’ armor could not withstand such firepower.
Sheinbaum’s response — measured but pointed — follows a pattern her government has maintained since taking office: insisting on what Mexicans call corresponsabilidad, or shared responsibility.
Mexico has long argued that the “iron river” of American weapons flowing south is the mirror image of the northbound drug trade, and that Washington cannot credibly demand action on fentanyl while its own regulatory gaps arm the very organizations it claims to fight.
According to U.S. Justice Department data cited by Mexico, 75 percent of weapons seized in the country originate in the United States.
The revelations land at a uniquely combustible moment in the bilateral relationship. In June 2025, the U.S. Supreme Court unanimously blocked Mexico’s $10 billion lawsuit against American firearms manufacturers including Smith & Wesson and Colt, ruling that the companies’ conduct did not constitute the kind of aiding and abetting required to bypass federal immunity protections for the gun industry.
That verdict, while narrow in legal scope, effectively closed the courtroom route Mexico had pursued since 2021. The Lake City investigation shifts the spotlight from private manufacturers to a government-owned facility — a distinction that carries different political and legal implications, and hands Sheinbaum a powerful new argument in the ongoing diplomatic tug-of-war over who bears responsibility for the violence.
In September 2025, the two countries launched “Mission Firewall,” a bilateral initiative to combat firearms trafficking that included real-time intelligence sharing, expanded forensic tracing across all 32 Mexican states, and increased southbound border inspections.
Sheinbaum hailed it as a breakthrough — the first time Washington formally committed to conducting anti-trafficking operations on its own soil. Yet the broader context remains defined by confrontation.
The Trump administration designated several Mexican cartels as foreign terrorist organizations in February 2025, and since September the U.S. military has conducted lethal strikes on suspected drug-trafficking vessels in international waters.
In January 2026, Trump told Fox News the United States would begin “hitting land” in Mexico — a threat Sheinbaum has flatly rejected. “We do not accept an intervention by any foreign government,” she has said repeatedly.
Sheinbaum also reiterated Monday that American drug consumption must be addressed as a public health crisis through education campaigns aimed at reducing demand — a position that resonates deeply in a country exhausted by the framing of the security crisis as a problem Mexico alone must solve.
A U.S. Army spokesperson, for its part, defended Lake City’s commercial sales by saying they save taxpayers approximately $50 million annually.
In Michoacán, Brenda Aparicio Villegas still mourns her husband, one of thirteen police officers killed in a 2019 cartel ambush. Investigators found Lake City casings at that scene too. Her husband and his colleagues often had to purchase their own bullets, she told ICIJ.
They never stood a chance against .50-caliber rifles. “Sadly,” she said, “many of us pay the price.” It is the kind of line that lingers — a verdict on a relationship where both nations export the ingredients of the other’s crisis, and neither has fully reckoned with the cost.
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