(NewsNation) — Law enforcement is working to stop drugs from crossing the Mexico border into the United States, but Mexico faces its own challenge — violence carried out with guns trafficked from the U.S.

Gun smuggling from the U.S. to Mexico is a well-documented practice, and Mexico’s leaders have long called for stricter firearm laws on the U.S. side of the border.

Just this week, a gun-running operation that spanned multiple states and several years resulted in the arrests of two Ohio men.

Federal authorities believe the two suspects were involved in a scheme to sell at least 90 rifles in Florida and Cleveland to people they believed worked for Mexican cartels.

Just as much of the illicit fentanyl fueling America’s drug crisis can be traced back to Mexico, the guns used in acts of violence over the border often originate in the U.S., retired Homeland Security Investigations division chief Joseph Lestrange told The Trace.

“(Gun trafficking) fuels and facilitates the continued expansion of criminal enterprises in Mexico that are feeding this demand,” he said.

Experts say cross-border firearm sales only help further drug activity and cartel violence. Rather than having the U.S. intervene, however, Mexican President Andrés Manuel López Obrador has instead suggested the U.S. tend to its own “social decay.”

Others have argued that Mexico’s own strict gun laws create a demand for illicit sales. The country has only one gun store and it’s located on an Army base. Still, Mexico’s homicide rate is more than 4 ½ times the world average and so far, no agency has fully developed a way to measure its ability to disrupt firearm trafficking to Mexico.

How many guns?

U.S. Customs and Border Patrol seized 902 firearms leaving the country last year — a drop in the bucket compared to the estimated 200,000 firearms trafficked from the U.S. into Mexico each year.

Those weapons ultimately contribute to organized crime violence by helping the illicit drug trade, according to the U.S. Government Accountability Office (GAO). The GAO analyzed the cross-border gun-running between 2014 and 2018 — the most recent analysis available.

A separate ATF analysis found 70% of firearms recovered in Mexico originated from the U.S. between 2014 and 2018, the most recent data available form Mexico.

More recently, the ATF found estimated 27% of international crime guns recovered between 2017 and 2021 could be traced back to a U.S. purchaser.

“These are firearms that were recovered by Mexican law enforcement officials and that were either used in a crime or may be found at the scene of a crime,” said Chelsa Kenny, director of international affairs at the GAO.

It can be difficult to trace guns back to the original owner because of how the guns are purchased. In fact, more than 70% of guns the ATF examined couldn’t be traced back to the initial buyer.

“They were likely purchased from consignment shops like pawn shops, or maybe from person-to-person transactions,” Kenny said. “So they’re actually unable to even trace it back to that original purchase.”

In other cases, the ATF received incomplete or inaccurate information from the Mexican police departments that recovered the firearms, or in fewer instances, the serial number on the weapon was obliterated.

Who’s smuggling them?

Pinpointing who exactly is responsible is challenging because of so-called straw purchases, untraceable sales and inconsistent data collection.

In the case that led to the arrest of two Ohio men this week, ATF agents posed as Mexican cartel members arranged to buy at least 90 rifles and one machine gun with a silencer from the suspects. Following their arrests, both men admitted to agents they were trafficking firearms, according to a news release.

Guns are diverted to the illegal market in Mexico after individual buyers purchase multiple firearms from a dealer, federal authorities believe. That buyer then traffics the gun to the person who wants it, according to the GAO.

Trafficked guns have included .50 caliber sniper rifles that can shoot down helicopters and penetrate lightly armored vehicles and bulletproof glass.

“They’re used to protect drug trafficking routes or illicit proceeds profits from drugs, and also drug processing locations,” Kenny said. “And then of course, they contribute to significant amounts of violence both in Mexico and the United States.”

Tracking smugglers is an arduous task that spans several initiatives across multiple agencies including the ATF and the Department of Homeland Security Investigations.

But the disjointed nature of the investigations means each agency only captures part of the picture, and agents may struggle to identify patterns to help intercept firearms.

“It’s not a one-and-done kind of analysis,” she said.

What’s being done to stop it?

Over the years, different federal agencies have taken their turn trying to get in front of firearm trafficking.

Most recently, Mexico and the U.S. entered into a new bilateral agreement in 2021. Now, unlike previous years, stopping and prosecuting firearms trafficking is explicitly listed a shared goal between both countries.

“It actually has a specific responsibility for the US to take greater efforts in addressing firearms trafficking, and I hope that data analysis and strategic approach is part of that,” Kenny said.

Meanwhile, Mexico has taken its own approach, twice filing lawsuits against U.S. gun manufacturers.

“A small minority of gun dealers — fewer than 10% — sell about 90% of crime guns,” attorneys wrote in a federal civil complaint filed in October against five Arizona gun sellers.

Mexico’s October lawsuit accuses a group of Arizona gun sellers of violating Mexican import and U.S. export laws as well as U.S. regulations against straw firearm purchases.

Last summer, a judge dismissed a similar lawsuit filed in Massachusetts, after ruling the U.S. Constitution protects gun sales.