SAN DIEGO — The 21-year-old who carried out a devastating and racist rampage at an El Paso Walmart a month ago chose a powerful AK-style rifle to commit what's believed to be the deadliest attack targeting Latinos in recent U.S. history.

The weapon he used is also the gun of choice of Mexican cartels, and it's used to kill hundreds if not thousands of Mexican citizens every week.

Each year, tens of thousands of powerful assault rifles are illegally trafficked from the United States into Mexico, mostly by U.S. citizens, where they are used to support cartel-related violence and drug trafficking.

More than 33,000 people were murdered in Mexico last year, a record annual total. In Tijuana, a city that saw more than 2,500 homicides last year, earning it the title of "the most violent city in the world," nearly every single gun seized by police since 2016 came from the United States, according to the city's chief of police.

Mexico's president, Andrés Manuel López Obrador, has urged the United States to enact gun control.

"We are very respectful of what other governments decide, but we think these unfortunate events in the United States should prompt reflection, analysis and the decision to control the indiscriminate sale of guns," López Obrador said days after the shooting.

The Mexican government announced in late July a major new joint operation with the United States to crack down on cross-border gun trafficking. Details remain murky, and the U.S. has not confirmed it has signed on to participate in the new effort.

Mexican Foreign Minister Marcelo Ebrard has highlighted five border crossings — San Diego-Tijuana; El Paso-Ciudad Juárez; Laredo-Nuevo Laredo; McAllen-Reynosa; and Brownsville-Matamoros — where the United States and Mexico would try to stem the flow of the more than 200,000 firearms smuggled south every year.

Ebrard, speaking in Mexico City, said the number of machine guns seized at crime scenes in the country jumped 63% in early 2019, and the number of assault weapons has surged 122%.

The illegal traffic of U.S. guns into Mexico — an underground market worth hundreds of millions of dollars — fuels nearly all of the country's skyrocketing violence, according to law enforcement officials on both sides of the border.

The U.S. Congress will soon renew its decadelong debate over gun control in the wake of several recent mass shootings, including one Saturday in Odessa, Texas, in which seven people were killed and about 25 injured.

Democrats on the House Judiciary Committee will return early from summer release — Wednesday — to consider gun-violence legislation. Chairmen of Senate panels are reviewing possible bills for consideration after recess.

Jack Riley, a retired DEA agent, said Mexican cartels prefer American-made guns for two reasons: they work, and they are a status symbol.

"It is really important to these criminal organizations, who stay in business by the threat of violence and through the use of violence; and the tools that they prefer to do that with are American-made guns," said Riley, who wrote the book "Drug Warrior" about his time as the DEA special agent-in charge, leading the manhunt for cartel boss Joaquín "El Chapo" Guzmán.

Riley said U.S. citizens trafficking American-made guns through Mexican ports of entry along the U.S.-Mexico border, including through San Ysidro-Tijuana, is big business.

"There is a tremendous market for them, and unfortunately there's a ton of people in the United States willing to do business with some of the cartels," Riley said.

A report from the U.S. Government Accountability Office showed that 70% of guns seized across all of Mexico have U.S. origins.

During his weekly press briefings, Tijuana's public safety director, Marco Antonio Sotomayor, has taken to emphasizing the United States origins of each AK-47, AR15 and Glock confiscated by police battling the city's raging drug violence.

"There's no way for people to buy guns like these in Mexico. They're American-made guns. We know they're being illegally trafficked through California into Tijuana," Sotomayor said.

Mexico's Constitution grants its citizens the right to own guns. But in practice, obtaining a firearm is very difficult under the country's strict gun laws.

Only the military is permitted to own high-caliber assault rifles in Mexico.

Any weapon more powerful than a .38 caliber is banned from personal use. Person-to-person firearm sales are also prohibited.

There is only one legal gun store in the entire country. It's in Mexico City and run by the Mexican army, which is the only agency permitted to sell guns to anyone in the country. Civilians must undergo a six-month background check.

Between 2013 and 2018 only 218 licenses to carry guns were issued nationwide, according to the Secretariat of National Defense, Mexico's equivalent of the U.S. Department of Defense.

In Tijuana, police seize dozens of illegal firearms each week.

In July, Mexican soldiers stopped a California SUV carrying an arsenal of large-caliber machine guns and rifles in Ensenada. The truck, heading south from California, was carrying six heavygauge machine guns inside, along with skilled cartridges, six tactical bibs, six AR-15-style rifles, 43 AR15 loaders and 1,290 cartridges.

Police on both sides of the border say Mexican immigration officials need better training, equipment and resources to stem the flow of guns into the country.

"They don't have the manpower. They don't have the X-ray equipment, and then always in the back of their minds, there is legitimate commerce going both ways that they have to regulate. So many of the things we're dealing with at our ports of entry, they are too," Riley said.

The Mexican state of Baja California has deployed 300 members of a newly formed National Guard to high-crime areas in Tijuana partly to target illegal drug trafficking into the country.

Riley said neither country will have success stemming the problem unless law enforcement works together from both sides of the border.

"It really is a bilateral issue that needs to be addressed consistently, and I think the scary thing about it is we're not sending a message to the cartels and the drug traffickers that we're even working together," he said.

This report includes material from the Associated Press.

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