MEXICO CITY (AP) — When four Americans were kidnapped in the border city of Matamoros, authorities rescued the survivors within days, but thousands of Mexicans remain missing in the state long associated with cartel violence — some in cases dating back more than a decade.

Mexican authorities quickly blamed the local Gulf cartel for shooting up the Americans' minivan after they crossed the border for cosmetic surgery Friday. They found the Americans — two dead, one injured and one apparently unharmed — early Tuesday after a massive search involving squads of Mexican soldiers and National Guard troops.

By contrast, more than 112,000 Mexicans remain missing nationwide, in many cases years or decades after they disappeared. Although a convoy of armored Mexican military trucks extracted the Americans, the only ones searching for most of the missing Mexicans are their desperate relatives.

"If these people had been Mexicans, they might still be disappeared," said Guadalupe Correa-Cabrera, an associate professor at George Mason University.

The rescue of the Americans provoked a special kind of fury in Tamaulipas, a border state long dominated by the warring Gulf and Northeast cartels, where the Network of Disappeared activist group estimates that 12,537 people remain missing.

Delia Quiroa, from the nearby city of Reynosa, has been looking for her brother Roberto for nine years, ever since he was kidnapped by gunmen — probably belonging to the Gulf cartel, the same group blamed for abducting the Americans — in March 2014.

Despite carrying out their own searches and pressuring authorities to investigate, the family knows nothing about his whereabouts.

Quiroa said that the families of the missing "celebrate and give thanks to God that they found these four U.S. citizens," but said "we wish the government would search for our disappeared with the same zeal and diligence."

"We feel complete indignation, desperation, anguish, impotence and grief," Quiroa said, because of "authorities' failure to act when Mexican families suffer the disappearance of a relative."

Volunteer search teams like Quiroa's often are forced to walk the deserts of northern Mexico with iron rods and shovels, looking for clandestine graves where the bodies of the relatives may have been dumped.

Authorities lack both the manpower, equipment and training — and many say, the will — to investigate the abductions, much less arrest or punish those responsible. Things are so bad that authorities aren't even able to identify tens of thousands of bodies that have been found.

Like everything else, the fact that Americans were involved in the most recent abduction may guarantee that Mexican authorities go after the killers. About two dozen suspects, most from the Juarez cartel, have been arrested in connection with the 2019 killings of nine U.S. citizens — women and children — in the western border state of Sonora.

It is unclear exactly what faction of the Gulf cartel may have abducted the Americans in Matamoros last week. The gangs go by colorful nicknames like "The Scorpions," "The Cyclones" and "The Troops of Hell." In Matamoros, Correa-Cabrera said, they are essentially all offshoots of the Cardenas clan, whose head, Osiel Cardenas Guillen, was arrested in 2003.

The gangs care little about innocent bystanders. In 2021, gunmen from factions of the Gulf cartel drove through the streets of Reynosa randomly killing 15 passersby just to intimidate their rivals.

The Mexican government claims that its "hugs not bullets" strategy — anti-poverty programs intended to reduce the number of recruits for drug gangs — has been working. The number of officially recognized homicides fell from 719 in 2020, to 707 in 2021 and 492 in 2022.

That, of course, doesn't count all of the disappeared people. But things are clearly not as bad as the dark days of 2010 and 2011 in Tamaulipas, when drug cartels massacred 72 migrants or dragged passengers off passing buses and killed hundreds who refused to fight each other to the death with sledge hammers.

Correa-Cabrera said the decline in killings and crimes in Matamoros in recent years may have been because the Cardenas clan re-asserted control.

"It was clear that the Cardenas family had control of the territory and there was a peace, a sort of mafia peace" in Matamoros, Correa-Cabrera said, until early this year when it appeared to break down.

"At the start of this year, there began to be reports of a lot more extorsion by the same group that controls the city," said the professor, who previously taught at the then University of Texas-Brownsville just across the Rio Grande from Matamoros.

It is clear that the events have unnerved U.S. officials, who have to tread carefully given the nationalistic bent of President Andrés Manuel López Obrador's administration.

The United States depends on the Mexican government to help control the influx of migrants from South and Central America but also watches helplessly as Mexican-made fentanyl flows across the border, causing about 70,000 overdose deaths in the United States each year.

In a rare criticism, U.S. Ambassador Ken Salazar wrote in his Twitter account Tuesday that "we are particularly worried about the control that the Gulf cartel exercises over an area known as the frontera chica," which is near Matamoros.

The Mexican government is likely to feel pressured to at least investigate those involved in the Americans' case.

"Cartel violence predated the (López Obrador) administration, of course, but the policy of 'hugs not bullets' is not yielding the promised results as evidenced by increasing violence," said Andrew Rudman, director of the Wilson Center's Mexico Institute.