On August 24, an armored U.S. embassy SUV was attacked in the mountains south of Mexico City. Gunmen pursued the vehicle at high speeds, riddling it with bullets and wounding two of the occupants. Now the mysterious attack has become even more troubling.

It was the fourth significant attack in the past few years on U.S. government personnel stationed in Mexico. In March 2010, Lesley Enriquez Redelfs, an employee of the U.S. consulate in Ciudad Juárez, was shot to death in her car along with her husband, Arthur, in broad daylight after leaving a children’s party sponsored by the U.S. consul. The husband of another consular employee was killed and their two children seriously wounded on the same day in a separate drive-by shooting. Jaime Zapata, a special U.S. Immigration and Customs Enforcement agent on assignment to the U.S. embassy in Mexico City, suffered a similar fate in February 2011. Zapata and another ICE agent were returning to the capital after meeting with law-enforcement officials in the northern state of San Luis Potosí when they were ambushed.

But while those previous attacks clearly were carried out by hitmen employed by the violent Mexican drug cartels, the perpetrators of this assault appear to be twelve members of Mexico’s federal police. The circumstances of the pursuit and attack seem to rule out the scenario of mistaken identity. Although the exact reason for the attack has yet to be established, the most likely explanation is that the incident is the latest case of penetration of Mexico’s police forces by the cartels. Indeed, the New York Times reports that the “embassy personnel” in the SUV were CIA agents assisting the Mexican Navy in antidrug efforts, giving the cartels an obvious motive for ordering an attack. And the Washington Post quotes President Felipe Calderón as believing that the federal police involved had “ties to criminal organizations.”

It would certainly not be the first high-profile case of supposed law-enforcement personnel doing the bidding of the criminal syndicates. It is a long-standing problem. In February 2000, Tijuana’s police chief was assassinated, and a short time later, seven men, including two former members of the Tijuana police force, were arrested for the chief’s killing. The men confessed to working for the Sinaloa cartel. In another incident, a bloody gun battle ensued in downtown Tijuana when police attempted to stop a drug trafficker’s armed motorcade. The commander of the police unit and three officers were killed by the trafficker’s bodyguards. Those bodyguards, it turned out, were local police officers.

The administration of President Vicente Fox (2000–2006) made a valiant effort to crack down on police who had been co-opted by the drug cartels. At one point, more than seven hundred officers were charged with offenses ranging from taking bribes to drug-related kidnapping and murder. Yet those arrested represented only the tip of a very big iceberg of corruption.

Both violence and police corruption in Nuevo Laredo reached the point in June 2005 that Mexico’s national government suspended the city’s police force and sent in the federal police to patrol the streets. Federal authorities proceeded to purge the local police, eventually firing 305 of the 765 police officers—forty-one of them for attacking the federal police when those units arrived in the city.

Matters across the country have not improved since then. In July 2009, nearly eighty police officers were arrested in eighteen towns across the state of Nuevo León after soldiers found their names on an organizational roster captured from traffickers. Just before Christmas of that year, soldiers discovered a list of dozens of police in Monterrey, Mexico’s leading economic city, who were apparently on the payroll of traffickers—in some cases working as hit men.

Edelmiro Cavazos, the mayor of Santiago, a quaint tourist town a few hours from the U.S. border, certainly discovered that he could not trust his own police force. On the night of August 15, 2010, Cavazos was abducted from his home while his wife and children were visiting relatives in Texas. Two days later, his corpse was found dumped by the side of a road. He became one of fourteen mayors killed in 2010, but his murder was not the only awful aspect of the episode.

The security surveillance system showed one of the police officers assigned to guard the mayor’s house walking out to meet an approaching convoy of cars. Armed men emerged from those vehicles and walked up to the front door. When Cavazos answered the door, the gunmen threatened him with drawn weapons, forced him outside and pushed him into the back seat of the lead vehicle. The subsequent investigation implicated the guard and five other officers for involvement in Cavazos’ kidnapping and assassination.

Given that track record, it would not come as a great surprise if the investigation of the recent attack on the U.S. embassy employees shows that the federal police were doing the bidding of one of the cartels. The corruption in Mexico’s police forces runs very deep, and it grows steadily worse.

Nor is the situation with the country’s military much better. It should be remembered that the notorious Zetas cartel began in the late 1990s as a specially trained elite commando unit of the Mexican military. Indeed, the United States provided much of the training of that unit at Fort Bragg, North Carolina. Most of the individuals who have joined the Zetas in the intervening years are former police or military personnel.

The harsh truth is that Mexico’s drug cartels are becoming stronger and more dangerous, and the law-enforcement and security agencies arrayed against them are riddled with turncoats and infiltrators. That is not surprising, since the drug syndicates have an estimated $35 billion to $60 billion a year in income at their disposal. Such a vast sum gives them an enormous capability to corrupt those people who are assigned to oppose them. The United States faces an increasingly troubling security situation on its southern border.

Ted Galen Carpenter, a senior fellow at the Cato Institute, is the author of nine books and more than five hundred articles and studies on international affairs. His latest book, The Fire Next Door: Mexico’s Drug Violence and the Danger to America, is forthcoming in October 2012.

Image: AlejandroLinaresGarcia