The drug industry managers move inconspicuously. The cartels' heads live like ghosts. Everyone fears them, but hardly anyone has seen one. The most powerful drug lord in the world, El Chapo Guzmán, head of the Sinaloa cartel, dared to go out in public for the last time seven years ago, according to eyewitnesses. He walked into a restaurant in Nuevo Laredo with 15 bodyguards, barricaded the door from the inside, collected the mobile phones of the 30 other customers and said, "Hello, nice to meet you. How are you? I am Joaquín Guzmán Loera. It's an honor." He ate steak and shrimp, paid for the other guests' meals and then disappeared.

Martinez learned that smuggling drugs is similar to boxing. His problem was that the cartels fight in a much higher weight class than Americans. They have more money, more power, more experience, and no rules.

"You have to meet Psycho," says Martinez. "He has lived through it all with me."

Psycho's real name is David Cordoba, and he used to be Martinez's partner at the DEA. His friends call him Psycho because he once allegedly rode a horse into Tiffany's Bar to order a beer. The DEA dismissed him when he wrecked his car while drunk on duty. Martinez meets him in a bar 50 meters from the border fence. Psycho is now working as a bodyguard for business people who want to travel to Mexico. On this day, he is welcoming the afternoon with a few beers.

Martinez and Psycho hug, holding on to each other tightly for a long time. "Come on, we're going to Juárez," says Psycho. "I'll get us an armored car and we'll speed through the streets like we used to." Martinez looks right at Psycho for a few seconds, then refuses.

He always feared his work in Juárez and remembers the day when his boss phoned him and Psycho in the office and said, "Guys, there is a fire on the other side of the river and we need to put it out."

In 1995, the year when Martinez went to Juárez for the first time as an agent, the American president at the time, Bill Clinton, said that the country must do more to prevent drugs from coming in. Martinez saw it that way too.

Bending the Rules In one of his first assignments, which he carried out together with the Mexican police, he was there when a commandant arrested a dealer. The police led the prisoner to a house on the edge of town. The officer hauled the prisoner to the bathroom, put his head in the toilet and flushed three times, says Martinez. The prisoner remained silent. The officer put a plastic bag over the prisoner's head. "Who paid you? Who paid you, cabrón?" he demanded. Then, to Martinez, he said: "Have you seen enough?"

When he got into his car to leave, Martinez watched in the rearview mirror as a Mexican police officer took a small rod out of his car trunk. Martinez had seen a rod like that before; it was an electric cattle prod.

That look in the rearview mirror was the moment he began to consider what had become of his goal to do good. He told himself that every day he won his battles and that the country could be proud of him. But when would the war finally be won?

When he came home, he kissed his wife Susie, a teacher, and said, "Hey honey, it was a good day, nothing particular to report from me today."

He thought he had drawn a line between work and private life, between Martinez the cop and Martinez the human. But the criminal energy that he fought each day infiltrated his thoughts.

It started when he searched houses without a warrant. If he found drugs, he picked up the search warrant afterwards. He arrested a Mexican that he knew was working in the middle management of a cartel. He had no proof; he just knew it. After three weeks on trial, the court had to let the manager go free. So Martinez told the Mexican commandant what that man looked like and when he would be freed. After he crossed the border, a black minibus on the Mexican side stopped beside him and took him away.

"Alright," says Martinez, taking a deep breath. So far he has laughed a lot on his journey through the memories. But he tells the next chapter without looking up, describing operations that weren't recorded in any files.

"A lot of people disappear in Mexico," he says. "They are buried where no one will find them. Some are eaten by tigers and some by sharks. There are also big tanks with acid in them." He pauses for a long time between the sentences.

"We didn't manage to catch all the bad guys. In those cases, we gave the Mexicans their names and said, 'Do what you need to do.' The Mexicans made those people disappear."

Martinez sits in his car, holding the steering wheel firmly with both hands. He looks frightened by the memories of his own life. "Come on, let's go to the cemetery," he says.

The Drug War Gets Personal

His cousin Bruno is in this cemetery. He was 27 years old when he was shot and killed on Martinez's wedding anniversary. He was struck in the torso by two bullets while crossing a shopping center parking lot. Police caught the shooter that same evening -- a 13-year-old boy from Juárez who named no motive.

"Please Sal, go get him," a cousin told him at the funeral. Martinez visited the killer's mother in the slums of Juárez to find out why the shooting had occurred, but she was silent.

Three years after Bruno's death, the phone rang in Martinez's office. He was with an informant, a police officer from Mexico, Jaime Jañez, who sold him information about cartels. It was Susie, who said that the killer had been released and was back in Juárez.

Martinez hung up the phone and said nothing. Jañez said he knew a few people in Juárez who owed him a favor. Martinez and Jañez met up a few more times, and Martinez paid him a total of $10,000 of the DEA's money intended for information. One day Jañez asked whether Martinez wanted the boy killed, and he said yes.

A few weeks later, Martinez was sitting with two FBI agents in a room during a training session. He thought the men were going to tell him something about the cooperation between the DEA and the FBI. Instead, they read him his Miranda rights.

They asked Martinez if he wanted to tell his story. He replied that he wanted to speak with his lawyer.

He doesn't know why Jañez gave him up. Perhaps because he was a law-abiding citizen, or perhaps the FBI paid handsomely for such information. Jañez was wearing a wire during their meetings, and the FBI had them on tape and video. Martinez pled guilty and the court sentenced him to 87 months in prison for attempted murder.