Last year, more Mexicans were killed with guns than in any year on record. Most of those guns came from the US.

The massacre in Parkland, Florida and the massive protests it inspired have rightly highlighted how military-grade assault weapons, along with high-capacity magazines, should not be sold commercially. These types of rifles produce greater damage in their human victims, and their ease of rapid fire has made them a weapon of choice in mass shootings in the United States.

It is true that handguns are used in the vast majority of gun homicides in the US. But in Mexico, assault rifles are the preferred weapon for organised crime, which seeks military assets to control territory, as Al Jazeera’s Juliana Ruhfus found in the investigation for her film “America’s Guns: Arming Mexico’s Cartels” that aired earlier this month. The result of the steady flow of assault weaponry into Mexico has only gotten worse. Last year, Mexico opened 16,828 gun homicide investigations – more than in any year of its recorded history, and more than in the entire US, even though Mexico has less than half the population of its northern neighbour.

Most of the guns used in those crimes came from the US – 70 percent of guns recovered at crime scenes in Mexico and traced since 2009 were purchased in the US and trafficked across the border. Doing so is easy, since the US-Mexico border is designed principally to facilitate massive volumes of trade. The Border Patrol, fences, and militarised infrastructure on that border are to stop migrants moving from south to north, not threats that move from the US into Mexico.

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The human toll in Mexico from the gun trade is devastating. Dr Marvin Hernandez Ortega and three other young professionals were travelling on the federal highway near Acapulco on June 19, 2015, when they were forcibly disappeared. Five days later, local authorities found bodies that they said were the young men’s. Near their burned-out vehicle, shell casings from assault rifles were found. “These weapons are instruments of the growing violence and homicides in Mexico,” Hernandez Ortega’s uncle, Romualdo Hernandez, told me when he visited Washington in 2016. “We demand that the US government exercise control over the weapons companies and border crossings.”

To reduce the flow of weaponry that feeds violence in Mexico requires looking not only at the border crossings themselves, but upstream – to the production of and legal access to weapons made for killing people. That is why it is important for the US Congress – and failing that, southern border states – to prohibit assault weapons and high-capacity magazines, and to make gun trafficking itself a crime.

The problem is cultural and ethical, as well as one of policies and laws. While hundreds of thousands of people in 800 cities and towns in the US marched for legislation to prevent gun violence last Saturday, gun company Sig Sauer was showing small children how to shoot pistols and sniper rifles with silencers at the Game and Fish Expo in Arizona – a state that is ground zero for the legal and illegal export of guns to Mexico.

The legal export of guns by US gun producers to Mexican police is also feeding criminal activities and the illegal gun market in Mexico, in several ways. The Mexican military is the only legal importer of firearms in Mexico; in turn, it sells weapons to police throughout the country, and, to a lesser extent, to private individuals and security companies.

State and local police in Mexico have had more than 20,000 firearms go missing or stolen since 2006, according to Mexican military documents. More than 8,000 rifles and handguns disappeared during that time from police arsenals in the city and state of Mexico and Guerrero state alone. In Guerrero, infamous for corruption and human rights violations by its police and military, out of every five firearms legally acquired by police, more than one went missing or stolen.

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US exports of weapons to the Mexican armed forces have grown enormously as part of the militarised security strategy that has disastrously failed to reduce homicides. The use of state weapons in operations to decapitate the leadership of criminal organisations has provoked more violence among prospective successors, while also feeding an arms race between criminal groups and the parts of the state that fight them. In addition, many Mexican police armed with US weapons directly commit human rights violations. The local police who attacked students from the Ayotzinapa teachers school and disappeared 43 of them in 2014, for example, were armed with AR-15 rifles exported by Colt Industries in Connecticut, according to court records.

When police collude with criminal organisations by giving them information or fighting their rivals in exchange for money, they are strengthening organised crime, even without directly trafficking weapons to it. US gun exports to Mexico thus strengthen the very forces, in many instances, that the arms sales are supposed to combat.

The Trump administration plans to deregulate such sales further, which will likely lead to even more US weapons in the hands of corrupt or abusive military and police forces. The US should instead suspend gun export licenses to Mexico and reorient its security policy there.

In the US, given the failure of the federal government in Washington to adequately control the illegal gun market, there are important steps that state governments can take, especially the southern border states, where more than three out of four illegal guns in Mexico traced to the US are purchased, according to the Government Accounting Office.

When the federal assault weapons ban expired in 2004, the sudden, easy availability in Texas and Arizona of these military-grade rifles accelerated killing in northern Mexican communities, independent of the growth of the drug war in that period, causing hundreds of additional annual deaths, according to a New York University study. California, on the other hand, kept an assault weapons ban in place, and also requires universal background checks on gun sales, unlike Texas and Arizona. As a result, guns used in crimes in Mexico were traced to Texas and Arizona at more than three times the rate per capita, compared with California, between 2009 and 2014. “Since 40 percent of all Mexican crime guns comes from Texas, state leaders should step up to study and implement sensible solutions to the deadly problem of gun trafficking,” says Andrea Bauer of the group Texas Gun Sense.

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Eighteen members of Congress last year called on the governors of the four southern US border states to “institute greater controls over southbound commercial activity. Agencies charged with enforcing firearm laws should be provided effective mandates, funding, and leadership”.

For its part, Mexico can make stopping the border gun trade an important part of its bilateral agenda with the Trump administration, and reframe the failed drug war policies that further arm police without holding them accountable for abuses and collusion with criminal forces.

Regional representatives will meet next week in Mexico City to consider how to effectively confront international arms trafficking. Gun victims in Mexico need action, as badly as the Parkland students and other gun victims do across the US.

The views expressed in this article are the author’s own and do not necessarily reflect Al Jazeera’s editorial stance.