“I like what I do,” he told the police in a videotaped confession. “I don’t deny it.”

Mr. Reta was 13 when he was recruited by the Zetas, the infamous assassins of the Gulf Cartel, law enforcement officials say. He was one of a group of American teenagers from the impoverished streets of Laredo who was lured into the drug wars across the Rio Grande in Mexico with promises of high pay, fancy cars and sexy women.

After a short apprenticeship, the young men lived in an expensive house in Texas, available to kill whenever called on. The Gulf Cartel was engaged in a turf war with the Sinaloa Cartel over the Interstate 35 corridor, the north-south highway that connects Laredo to Dallas and beyond, and is, according to law enforcement officials, one of the most important arteries for drug smuggling in the Americas.

The young men all paid a heavy price. Jesus Gonzalez III was beaten and knifed to death in a Mexican jail at 23. Mr. Reta, now 19, and his boyhood friend, Gabriel Cardona, 22, are serving what amounts to life sentences in prisons in the United States.

Other young Americans in their circle who the police say worked for the Zetas have also ended up in prison, have fled into hiding in Mexico or have disappeared in the permanent way that people wrapped up in the Mexican drug trade tend to go missing.

In the minds of many Americans, the Rio Grande divides Mexico, a corrupt land where drug cartels often seem to have the upper hand, from the United States, a nation of law and order, where the authorities try to keep criminal gangs in check.

But the reality on the border is much more complex. The Mexican drug cartels recruit young men from both countries and operate their smuggling and murder-for-hire rings on both sides of the divide, though under slightly different rules of engagement.

That complexity was reflected in the short but bloody careers of Mr. Reta, Mr. Gonzalez and Mr. Cardona, who are linked to crimes in both countries, according to trial transcripts, court documents and interviews with detectives and family members.

While working as hired guns in 2005 and 2006, the three Americans lived in a house rented by their employers on Hibiscus Street in Laredo, according to testimony at Mr. Reta’s trial. Another crew of three assassins, all from Mexico, were also camped out there, awaiting orders, law enforcement officials said.

The Mexican government has been trying to crack down on the drug cartels, an effort that has left more than 10,000 Mexicans dead in the last 18 months. Some deaths are the result of shootouts between the cartels and the authorities, with both sides heavily armed. But the assassinations of drug dealers involved in turf battles and of police officers and army personnel who get in the way — the kind of work Mr. Reta, Mr. Gonzalez and Mr. Cardona did — also accounts for thousands of bodies.

The two teams of assassins took direction from Lucio Quintero, or El Viejon, a capo in the Zetas across the river, trial records show. They received $500 a week as a retainer and $10,000 to $50,000 for each assassination, and the triggerman was given two kilos of cocaine.

Detective Roberto A. Garcia Jr. of the Laredo Police Department said they all worked for Miguel Treviño, the leader of the Zetas in Nuevo Laredo, the Mexican city across the river from Laredo, who goes by the name El Cuarenta, which means Forty. (Many Zetas identify themselves by a number.)

In addition to their retainers, the assassins received perks. At one point, Mr. Reta was given a new $70,000 Mercedes, for a job well done. Family members described how the young men would go to parties hosted by cartel capos. To keep up morale, the drug leaders would raffle off automobiles, firearms and even dates with attractive women, the family members said, speaking on the condition of anonymity.

‘They Just Seduce You’

Most of the American youths were recruited in a discothèque, the Eclipse, on the main square of Nuevo Laredo just across one of two bridges that connect the two towns. It is a darkened dive where teenagers go to drink, dance and flirt while reggaetón thunders. But cartel members lurk there, too, watching for possible recruits, the police say.

“The cartels — they just seduce you,” said Detective Garcia, who with his partner in the Laredo Police Department, Carlos Adan, broke up the ring. “They wave that power, that cash, the cars, the easy money. And these kids all have that romantic notion they are going to live forever.”

Detective Garcia described Mr. Cardona as the ringleader of the American cell of assassins, a savvy, brash young man who orchestrated at least five murders in Laredo of people connected to the Sinaloa Cartel.

In a deal with prosecutors, Mr. Cardona eventually pleaded guilty to kidnapping two American teenagers — one of whom had drug-gang connections — in March 2006 at a Mexican nightclub, taking them to a cartel safe house and stabbing them to death with a broken bottle. Investigators say he had collected the victims’ blood in a glass and toasted La Santa Muerte, a personification of death worshiped by some Mexicans. A federal judge sentenced Mr. Cardona to life in prison in March.

His mother, Gabriela Maldonado, a home health worker, said Mr. Cardona had grown up with an abusive, alcoholic father, but had done well in school through eighth grade, when his father abandoned the family.

Then Mr. Cardona began to skip classes and hang out with drug users on Lincoln Street. Soon he was sent to juvenile prison for aggravated assault, and after that he moved out of the house. Overnight, it seemed, he appeared to have a lot of cash and showed up in different cars, his mother said. At first, he told his mother he was “a soldier,” then later he said he had become “a commander.”

“He was so intelligent — I don’t know what happened to him,” she said. “He always said when he was young that he wanted to be a lawyer.”

If Mr. Cardona was the brains of the group, Mr. Reta was the keenest to become a professional assassin, Detective Garcia said. In July 2006, Mr. Reta told detectives in a videotaped confession that he had participated in at least 30 killings in Mexico, a statement that the authorities there could not confirm.

Mr. Reta told Detective Garcia that he was 13 the first time he killed a man. He said he was asked to prove his loyalty by doing it in front of Mr. Treviño, and he told the detective that he had used a .38 Super pistol to shoot the man as he was being held down in a chair at a safe house in the state of Tamaulipas.

After that, killing became addictive, Mr. Reta told Detective Garcia, and he compared the feeling to the allure of candy to a small child. “There were others to do it, but I would volunteer,” Mr. Reta said in the taped interview with the police. “It was like a James Bond game.”

“Anyone can do it, but not everyone wants to,” he added. “Some are weak in the mind and cannot carry it in their conscience. Others sleep as peacefully as fish.”

Mr. Reta also told the police that he had attended a training camp in Mexico for six months, where he learned to shoot assault rifles and engage in hand-to-hand combat. One of his instructors, he said, was an Israeli mercenary. Mr. Reta was also proud of his marksmanship.

“If I cannot hit you in the forehead from a distance,” he boasted in his interview with the police, “I will kneel down in front of you and put my forehead against the muzzle of your gun. I will look you in the eyes while you kill me.”

No Longer a Good Boy

Family members say Mr. Reta grew up with nine brothers and sisters, living in a tiny wood house, propped up on cinder blocks, in a yard devoid of grass. His father worked construction; his mother was a hairdresser. Before the age of 12, he was a well-mannered boy, respectful of his elders, who did tolerably well in school and spent most afternoons playing ball in a nearby park.

But puberty changed him. Mr. Reta ran away from home, living for a time at a girlfriend’s house. He also began to get in trouble with the law. He was picked up for marijuana possession and spent a year in a juvenile prison for firing a gun in public. He also became fascinated with commandos and dreamed of joining the Navy Seals, a person familiar with his life said.

On frequent trips to Mexico, he was also becoming involved with the Zetas, a family member said, speaking on the condition of anonymity for fear of reprisals from drug dealers. On trips home, Mr. Reta described killings in Mexico that he had witnessed and, in some cases, participated in. “He sounded so excited when he talked about all these things he was doing,” the family member said.

Now Mr. Reta lives in a cramped cell at the Robertson Unit, a state prison in Abilene, Tex. Despondent over being sentenced to 70 years for two killings in Laredo, he paid a fellow prisoner to tattoo flames and horn shapes on his face, giving him a demonic look.

As he talks, his countenance shifts back and forth, from the deadpan of a street tough with emotionless eyes to the oddly innocent laugh and smile of a 19-year-old boy for whom everything is a lark. His voice is soft and melodic, even when his words are menacing.

Mr. Reta declined to comment on his career as an assassin in Mexico, though he neither denied nor recanted his previous statements to the Laredo police. He did say he was innocent of taking part in one of the two killings he was convicted of in the United States and predicted his name would be cleared on appeal. “Not everything they say about me is true,” he said.

Speaking of his upbringing, he said that to him and his friends, growing up in ramshackle houses on dirt lots, the narcotics traffickers were heroes. The poorest counties in America lie along the Rio Grande, and Mr. Reta recalled stealing gummy bears from a local candy shop with Mr. Cardona when they were children.

“You know, here, all the little kids that are young, they say, ‘I want to be a firefighter when I grow up,’ ” Mr. Reta said, “Well down there, they say, ‘When I grow up, I want to be a Zeta.’ ”

“You know, it’s the money, cars, houses, girls,” he said, pausing, “and you know that ain’t going to last a lifetime, that its going to end.”

A Botched Assassination

It is unclear precisely how many killings in Mexico Mr. Reta had a role in. The Mexican authorities arrested him on charges that he was one of four men, led by a former commander of the Nuevo Laredo municipal police, who in May 2006 attacked El Punto Vivo Bar in Monterrey with grenades and rifles, killing 4 and injuring 25.

Afraid a rival gang would murder him in a Mexican jail, Mr. Reta called Detective Garcia and a Drug Enforcement Administration agent, Chris Diaz, shortly after his arrest pleading to be extradited to the United States, where he was wanted for the murder of Noe Flores in January 2006.

Though he claimed he did not shoot Mr. Flores, he admitted to the police that he had driven the getaway car. Mr. Cardona did the shooting, he said, after Mr. Gonzalez got cold feet, sat in the backseat and watched the killing take place in the front yard of a house.

That confession was eventually excluded from the evidence against him, forcing a second trial, at which he was convicted on other evidence, including his fingerprints found on a cigarette case in the getaway car. His lawyer has appealed the conviction.

According to testimony at Mr. Reta’s second trial, the crew botched the assassination. The group had intended to kill Miguel Flores, but shot his brother instead. A woman working for the cartel had spotted the Floreses at a Laredo bar and called Mr. Treviño, who in turn telephoned the assassins.

Mr. Flores was not the three assassins’ first victim on American soil, the authorities say. The same crew, prosecutors say, shot and killed Moises Garcia, a reputed drug dealer and member of the Mexican Mafia prison gang, outside the Torta-Mex restaurant on Dec. 8, 2005, while his wife and child looked on. In March, Mr. Reta pleaded guilty to being the triggerman in that killing and was sentenced to 30 years.

Detective Garcia said Mr. Reta’s phone call from a Mexican jail was not the first time he had called. While investigating the Flores killing, Detective Garcia used evidence found in the getaway car to track down a tattoo artist who could identify Mr. Reta, Mr. Cardona and Mr. Garcia. Frightened, the tattoo artist tipped off the teenagers, who fled to Nuevo Laredo.

Mr. Reta then called Detective Garcia’s cellphone, getting the number from the calling card the detective had left with the tattoo artist.

“He said ‘You better stop the investigation into these murders,’ ” Detective Garcia recalled. “He threatened me and my family.”

Mexican Cartels Lure American Teens as Killers

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