Updated

I never thought I would end up in prison, let alone a maximum-security one. But that's exactly where I was on June 26, 2009.

It was an unbearably hot Friday morning in Abilene, Texas, about 180 miles west of Dallas. I was a bundle of nerves when I got up at 6 a.m., not having slept much the night before from the anxiety. My camera crew and I were soon driving to Robertson Unit state prison, on our way to meet a then 19-year-old Rosalio Reta.

— Catch a brand-new episode of "War Stories Investigates: Drugs, Money and Narco-Terror," Saturday, August 22 at 3 p.m. and 9 p.m. ET only on FOX News Channel

Reta, a convicted murderer, had agreed to his first on-camera interview for the episode I was producing for FOX News Channel, "War Stories Investigates: Drugs, Money and Narco-Terror." He is serving 70 years for two murders in Laredo, Texas. Investigators say he committed them on the orders of Mexico's most well-armed and vicious gang of cartel enforcers, Los Zetas.
His story is surreal, yet all too common.

Born in Houston to a hairstylist mother and father who worked construction, Reta said he had a good childhood as one of 10 children. He grew up like any other kid playing football, soccer and baseball, and developed a love for skateboarding which earned him the nickname "Bart," after Bart Simpson. Eventually, the struggling family moved to a working class neighborhood in Laredo. The city of 215,000 is one of those quiet and unique American border towns, less than 1/2 mile across the Rio Grande from Mexico. The border is a mere formality and most residents routinely travel back and forth between the two countries.

Reta told me that it was on one of those trips to Nuevo Laredo, Mexico, that "he got involved with the wrong people" and life started to quickly unravel. He was only 13 years old.

"Where I'm from, if you're not a cop, you're a drug dealer," said Reta. "If you're not a drug dealer, you work for a cartel. That's all there is down there."

According to one of the Laredo Police Department detectives who helped send him to prison, Reta was recruited by Zeta henchmen at a nightclub. "They like the lure... of the money, the power, the women, the vehicles," said Detective Roberto Garcia. "It's thrown... in their face."

The young recruit was groomed to kill at a special training camp run by a rogue band of Mexican Special Forces deserters, the original founders of the Zetas. The mercenaries act as enforcers for the Gulf Cartel. One of the top Zeta lieutenants is 38-year-old Miguel Trevino Morales — a ruthless trafficker wanted on both sides of the border.

"[Reta] was introduced to Miguel Trevino, [and] given his first execution at the age of 13," said Garcia. "It was to prove his manhood, that he could do it. And it's what he did."

In his July 2006 interrogation, Reta described the thrill of a kill to Detective Garcia as "a James Bond game" in which he would closely monitor his victims and wait for the right moment to pull the trigger. In his conversation with me, Reta said his preferred method of killing was "execution-style," and said that he was "fighting crimes" because if he didn't, he would be the target.

Kill or be killed. It was that simple.

Reta was part of the carnage in Mexico that has resulted in the deaths of 11,000 people. It is a classic turf war between rival drug cartels, battling for control of plazas or shipping corridors, straight into the heart of America — their biggest customer.

The Laredo/Nuevo Laredo smuggling zone is particularly lucrative; Interstate-35, which runs through it, provides fast access to Dallas and San Antonio, connecting all the way north to Chicago. It is a multi-billion dollar route worth protecting and that's what Reta was paid to do.

The two cartels vying to dominate his area of operations are Reta's own Gulf Cartel, and their arch enemy, the Sinaloa Cartel — whose members are known as Chapos, named after their leader, Joaquin "El Chapo" Guzman. Reta told me he once got $375, 000 for killing a Chapo bigwig.

Even though Reta refused to talk to me about his criminal career here in the United States, there is plenty of evidence — not to mention confessions and convictions — that indicate he was dispatched across the border to Laredo as part of a three-man assassination cell of American teenagers.

A spree of murders followed, at least five of which were physically linked to Reta's cell, eventually leading to the July 2009 indictment of his boss, Trevino. After a botched hit, Reta fled to Mexico to cool off and lay low.

It would prove to be the beginning of the end for him.

He went to a Mexican nightclub and threw some hand grenades after learning one of his "targets" was inside. Reta ended up killing four people and injuring 25. But he wasn't supposed to be there, so the Zetas caught and tortured him for insubordination.

"His own people wanted to kill him for disobeying orders," Garcia said.

According to Detective Garcia, he killed two of his captors and managed to escape by the skin of his teeth, a marked man. When he recounted the ordeal to me, however, he said the people who kidnapped him were actually rival cartel members, the Chapos.

Reta was eventually arrested in Mexico and extradited to the United States, a day before his 17th birthday. He was sentenced to 30 years after pleading guilty to the murder of Moises Garcia, a reputed drug dealer who had allegedly stolen narcotics from the Zetas. Reta was convicted of another murder — that of Noë Flores — and got 40 years, which is now on appeal. He remains hopeful, but I think he knows he will likely be in prison for the rest of his life.

There were times during the interview I thought, "Am I really sitting across from someone who has admitted he might have killed 30 people?" At no point was I scared or felt threatened by his presence. It was hard to believe the affable and soft-spoken young man was, just three years ago, operating as a contract killer in the American Southwest and neighboring Mexican states. Not even the sinister, flame-shaped tattoos all over his face make the now 20-year-old vegetarian look like an assassin.

"Even though he threatened to kill me, he comes across as a likable person," remembered Garcia.

But a trail of dead bodies tells a different story and Reta is left with all the time in the world to think about the decisions he made when he was an impressionable 13-year-old.

"If I would've stayed at my house, I wouldn't have been here," he said.

— Ayse Wieting is a producer for "War Stories"