The five men were left prostrate on the sidewalk outside their black pickup truck, their shirts pulled over their heads, bare torsos pressed against the ground, their bound hands spread before them almost in supplication.
The handwritten letter on the truck’s windshield read like a formal, albeit chilling and remarkable apology: the Gulf Cartel Scorpion Group was very sorry that their members accidentally shot and killed two Americans and a Mexican bystander while kidnapping two more U.S. citizens.
The men were being offered up to the authorities, the letter said, to make amends for disturbing the peace. On Friday, Mexican prosecutors charged the five men in connection with the abduction and killings.
While Mexican drug cartels thrive in a vacuum of law and order that persists inside Mexico, there is an unspoken rule that many members of organized criminal groups are careful not to cross: do not touch Americans.
The United States takes attacks on its citizens seriously, and the response to such violence, on both sides of the border, can be ruinous for a Mexican criminal group.
“When American citizens are targeted, it brings pressure from the U.S. government, they get their security agencies involved and then start putting pressure on Mexico to act,” said Cecilia Farfán Méndez, a Mexico security researcher at the University of California, San Diego.
“The worst thing for the cartels is that they have to dedicate resources to countering Mexican authorities that mostly leave them alone,’’ she added. “It’s not good for business.”
Cartels can often outgun Mexican authorities or simply buy their cooperation, but they know that prodding the U.S. government into action can hinder their ability to operate. And in recent years, organized crime has come to rely on the Mexican government’s inability to effectively control it.
Mexico’s president, Andrés Manuel López Obrador, came to office promising a new approach to quell violence: avoiding direct confrontation with criminal groups, in favor of addressing the root causes of criminality like corruption and poverty.
But his strategy, which he branded with the slogan “hugs, not bullets,” has done little to tame extraordinary levels of violence or diminish the ever-expanding power of cartels that traffic drugs and migrants across the U.S. border and terrorize Mexicans at home.
In many communities, Mexicans live in fear of criminal groups that commit daily acts of violence that by and large attract little attention outside the country. And while cartels avoid deliberately targeting Americans, their business model rests on shipping narcotics north that have helped fuel an epidemic of drug deaths in the United States.
The Biden administration has been reluctant to openly criticize Mr. López Obrador, including over security problems in Mexico, wary of threatening his cooperation on migration.
But the attack on four Americans last week became an international scandal, increasing pressure on the U.S. government to do more to combat crime south of the border, and eliciting calls from Republican lawmakers to authorize U.S. military force to confront the cartels.
The calls prompted an outcry in Mexico, with officials demanding that the U.S. government respect their sovereignty, but also forcing the Mexican government to respond. This week, hundreds of additional Mexican security forces were deployed to Matamoros, the border city where the attack on the four Americans unfolded.
That kind of outsize attention is precisely what criminal groups want to avoid, and they have largely left American citizens alone ever since the 1985 abduction, torture and brutal slaying of Enrique Camarena, a D.E.A. agent, who had disrupted cartel operations at the time and drew their bloody ire.
Mr. Camarena’s mutilated body was found wrapped in plastic bags on a ranch in western Mexico, his hands and feet bound and his face unrecognizable after multiple blows with a blunt object.
In its quest for justice, the D.E.A. launched Operation Legend, one of the largest homicide investigations undertaken by the agency, which revealed that Mexican authorities had covered up Mr. Camarena’s murder and destroyed valuable evidence. The operation led to the arrest of cartel members and forced others into hiding.
The message was clear: going after American law enforcement agents would have far-reaching consequences for criminals and their accomplices in the Mexican government.
Cartels eventually learned that even mistakenly killing U.S. citizens could be costly.
In 2019, an organized crime group opened fire on Americans and Mexicans who were driving through the northern state of Sonora, killing three women and six children, part of a Mormon group that lived in Mexico. Some of the victims were burned alive in their cars, about 70 miles south of the U.S. border.
In the aftermath, several people were arrested, including a Mexican police chief believed to be protecting local criminal groups. The Mexican government claimed the deadly attack could have been a case of mistaken identity and related to a conflict between two criminal groups vying for control.
This week, Mexican authorities were said to be considering a similar explanation for the kidnapping and slaying of the Americans in Matamoros, investigating whether it was another case of mistaken identity.
Those who live in Matamoros, which is part of the state of Tamaulipas and sits across the Rio Grande from the southernmost tip of Texas, endure the daily eruption of violence that consumes life here, ever since criminal organizations began consolidating control of the city.
What happened to the Americans is what they confront every day, Matamoros residents said, while dropping their children off at school, buying groceries or driving to work.
But what made this case different, they said in sorrow and anger, was the immense attention and pursuit of justice it received because of the victims’ nationalities.
“Who is talking about the woman who died here? No one,” said Alberto Salinas, referring to the Mexican who was shot and killed during the attack. Mr. Salinas owns a home next to the scene where the attack occurred, but was elsewhere at the time.
Tamaulipas is generally dominated by the Gulf cartel, one of the oldest criminal organizations in Mexico, but is carved up among different factions of criminal groups. Even if the factions all belong to the same overarching group, they are not always allied.
Local leaders are generally vigilant about who might be encroaching onto their territory. The Scorpions group, which claimed to have written the letter, originated as a special force that guarded a previous Gulf cartel leader, said Jesús Pérez Caballero, a security expert and professor at the Colegio de la Frontera Norte in Matamoros.
While Mexicans have often found letters from cartels accompanying corpses, the note left behind this week was rarer because the five men who were found with it were left alive.
Criminal organizations do police their own members, experts said, particularly if they draw too much attention to the groups’ activities.
Leaving the men alive could have been aimed at ensuring that they would give statements to investigators supporting the narrative that the cartel did not order the assault. Lower level members of such groups sometimes do act on their own, though it’s unclear if that’s what actually happened in this case.
“Many times the hit men try to show their merit to people with more power, and they go it alone and if it works out, it works out,” Mr. Pérez Caballero said. “And if it goes wrong, well, it goes wrong.”
Oscar Lopez contributed reporting from Mexico City.