VERACRUZ, MEXICO — The two thoroughbreds sprinted down a country track, a few million dollars in the bettors' kitty and an old-fashioned camera waiting at the finish line.
When the race was over, as veterinarians guided the expensive equines back to their air-conditioned trailers, gamblers at the private track began to argue over the nose-to-nose conclusion. Among them were members of a band of hit men known as the Zetas, employees of the Gulf cartel of drug traffickers.
Let's just wait for the film to be developed, someone said.
Then, above the din, another voice rang out. "I've come to kill you!"
A new chapter was being added to the violent saga of Mexico's most notorious drug ring. More than a dozen people may have been killed in the gunfire that followed, an ambush in which the hit men appear to have attacked one another.
The Zetas were Mexico's first drug cartel army, and in many ways they and their employers are responsible for the militarization of the country's drug conflict. President Felipe Calderon deployed the national army this year to fight traffickers in several Mexican states.
The March shootout at the Villarin track was one of many bloody episodes in what appears to be an escalating power struggle within the Gulf cartel. Experts say the increase in tension was triggered by the January deportation of reputed cartel leader Osiel Cardenas to face trafficking charges in the U.S.
"The cartel has split," Genaro Garcia Luna, public security minister and Mexico's top cop, said last week. "This has generated a new wave of violence as they fight over the regions Osiel controlled."
The cartel, based in the border state of Tamaulipas, grew wealthy and powerful thanks to the U.S. appetite for Colombian cocaine, and both of its branches remain potent forces in Mexico. Almost every week, a new act of cruelty, boldness or stupidity by the Zetas plays out in the country's tabloids and newscasts.
Before the 1990s, groups based in the Pacific Coast state of Sinaloa dominated Mexico's drug trade. The country's traffickers were becoming cash-rich as Colombian cartels increasingly ceded key smuggling routes into the U.S. to them.
To challenge the dominance of the Sinaloans, the ascendant Gulf cartel began recruiting soldiers from the army. The Zetas were born.
Their founder was a former army officer who had deserted: Lt. Arturo Guzman Decena, known as Zeta 1. He reportedly received training from the Israeli military.
According to the attorney general's office, Guzman is believed to have recruited several soldiers from his paratrooper brigade and at least 40 former members of the Mexican special forces.
"They brought the ideas of counterinsurgency and psychological warfare to the drug business," said Luis Astorga, an expert on the industry. "The idea is that if you paralyze your adversaries with fear, you've won half the battle."
The Zetas' mission was to wrest from Sinaloa and other groups the Gulf cartel's "right" to smuggle drugs through a given port or border city.
"The drug world is like any other business," Astorga said. "You try to take territory and profits from your rivals. But there are no courts to settle disputes. There is only violence."
The Gulf traffickers took advantage of the low pay and high desertion rate of the Mexican army, where one in eight soldiers deserts every year. Cartel members reportedly enticed the troops with large sums of cash and positions of responsibility, something the Sinaloa traffickers still shy away from.
"With the Sinaloa group, family ties have always been important," Astorga said. "To them, bringing in soldiers and giving them power was like admitting a Trojan horse into the fold."
Raul Benitez, a Mexico security expert at American University in Washington, says the Gulf cartel valued the army veterans for their knowledge of weapons and explosives. (In Mexico, the army regulates all firearms.)
As the Zetas gained strength, they brought increasingly powerful weaponry into the drug war, including .50-caliber machine guns originally designed as antiaircraft weapons. In recent years, grenade attacks on police stations have become common.
In popular legend, the Zetas are gunslingers with bazookas and military experience. They pull off killings that suggest a certain level of tactical training: In February, for example, they donned army uniforms to enter two Acapulco police stations and kill seven officers and employees.
But like many legends, the Zeta myth is built around a core truth that fades deeper into history each year.
Guzman -- Zeta 1 -- was killed in 2002 in a shootout with the army in Matamoros. As many of the other original hit men fell, the cartel sought new firepower, first recruiting members of the Guatemalan special forces, the Kaibiles.
Many of the original Zetas are dead or in prison, Mexican authorities say. U.S. officials say current members probably were recruited from the ranks of Mexico's urban and rural poor.