In Season 1 of “Narcos: Mexico,” the gruesome murder of DEA agent Enrique “Kiki” Camarena at the hands of drug lord Felix Gallardo (Diego Luna) was a turning point in the drug wars between Mexico and the US.

Camarena, played by Michael Pena, was kidnapped in 1985 by Jalisco police officers on Gallardo’s payroll and taken to his ranch. Two days later he was murdered when a hole was drilled into his head.

Enter Walt Breslin, a DEA agent with “carte blanche from the government to break the law and take it into his own hands,” according to Scoot McNairy, the Dallas-born actor who plays him in Season 2 of the Netflix series, premiering Thursday. “They didn’t’ want to be liable for it, but they gave the OK.”

McNairy, 42, debuted on the series last season as an occasional narrator and appeared on-camera in the season finale. This season, he expands his role through 10 episodes as Operation Leyenda — the homicide investigation’s official name — hunts down the men who worked over Camarena in hopes of catching Gallardo. McNairy was well-versed in the material, having seen all three seasons of the Colombia-based “Narcos,” which chronicled Pablo Escobar’s rise to power and eventual murder, and its Mexican counterpart.

“I was very excited to come on the show,” says McNairy.

In his research, the actor met with former DEA agent James Kuykendall, who worked alongside Camarena in Mexico and was played in Season 1 by Matt Letscher. He also interviewed contemporary agents. “Those guys are doing it now, but it was completely different 30 years ago,” he says. Ultimately, McNairy relied on the show’s writers, who he says, compressed the 10-year Operation Leyenda into the three years (1986-89) covered by Season 2.

Unlike Steve Murphy and Javier Pena, the real-life agents portrayed on “Narcos” by Boyd Holbrook and Pedro Pascal, Walt Breslin is not the name of a real agent. That doesn’t mean the character isn’t based on one, though. McNairy says Breslin was inspired by a guy who “was with the agency for 20 years and stayed on after Operation Leyenda was over,” but “I’m not allowed to say” his name.

Viewers will be dying to know that agent’s identity as Breslin and his team go to extremely unorthodox lengths to round up Camarena’s killers, which include a doctor who kept pumping the agent with adrenaline so he could remain conscious while being tortured. “In the past the DEA has had their hands tied,” he says. “This character is doing something different. We have to blame [Camarena’s death] on someone.”

Mexico City was the production hub for Season 2, but the series also filmed in Durango and Puerto Vallarta, among other locations. It was not McNairy’s first exposure to the cartel-ridden country. He filmed a 2010 film called “Monsters” there and saw the destruction that ruined the country first-hand. “It was horrific,” he says. “Kid coffins and caskets. I was beside myself. Why did the cartel come into this tiny town and kill all these people in this restaurant? So many people are killed every day. [Realizing] how many people had to die for one person to get high was a shocking experience.”

In reality, Gallardo was arrested in 1989 for Camarena’s murder and sentenced to 37 years in prison (he is still there). McNairy does get to act in one scene with Luna before the season wraps as Breslin and Gallardo face each other. “Both of those characters become a victim to the problem,” he says. “Walt gets what he wants, but all he does is trigger a bigger problem. They are just victims of the drug wars. You take away all the bells and whistles and stigmas of who these guys are and it really humanizes the characters.

“They are just real people doing what they have to do to survive.”