MEXICO CITY (AP) — Mexico’s National Guard officers on Wednesday arrested the hyper violent, alleged security chief for the “Chapitos” wing of the Sinaloa drug cartel.

The Public Safety Department’s arrest registry says Nestor Isidro Pérez Salas was detained around 1:30 p.m. Wednesday at a walled property in the Sinaloa state capital of Culiacan. The department listed his alias as “El Nini.”

The U.S. Drug Enforcement Administration in April had posted a $3 million reward for his capture. Pérez Salas is wanted on U.S. charges of conspiracy to import and distribute fentanyl in the United States. But he also allegedly left a trail of murder and torture behind him in Mexico.

“This guy was a complete psychopath,” said Mike Vigil, former head of international operations for the U.S. Drug Enforcement Administration. “Taking him out of commission is a good thing for Mexico.”

Pérez Salas allegedly protected the sons of imprisoned drug lord Joaquín “El Chapo” Guzmán, and also helped in their drug business. The sons lead a faction of the cartel known as the little Chapos, or “Chapitos” that has been identified as one of the main exporters of fentanyl, a deadly synthetic opioid, to the U.S. market.

Fentanyl has been blamed for about 70,000 overdose deaths per year in the United States.

Pérez Salas allegedly ran security for the Chapitos in Sinaloa state, according to prosecutors in the Southern District of New York. He was among nearly two dozen defendants named earlier this year in an indictment.

Pérez Salas commanded a security team known as the Ninis, “a particularly violent group of security personnel for the Chapitos,” according to the indictment unsealed in April. The Ninis “received military-style training in multiple areas of combat, including urban warfare, special weapons and tactics, and sniper proficiency.”

The nickname Nini is apparently a reference to a Mexican slang saying “neither nor,” used to describe youths who neither work nor study.

Pérez Salas allegedly participated in the torture of a Mexican federal agent in 2017. He and others tortured the man for two hours, inserting a corkscrew into his muscles, ripping it out and placing hot chiles in the wounds.

According to the indictment, the Ninis — the gang of gunmen led by Pérez Salas and Jorge Figueroa Benitez — carried out gruesome acts of violence.

The Ninis would take captured rivals to ranches owned by the Chapitos for execution.

“While many of these victims were shot, others were fed, dead or alive, to tigers” belonging to the Chapitos, “who raised and kept tigers as pets,” according to the indictment.

And while the Sinaloa cartel does some lab testing on its products, the Ninis conducted more grisly human testing on kidnapped rivals or addicts who are injected until they overdose.

In 2002, according to the indictment, the two Ninis leaders “experimented on a woman they were supposed to shoot” and “injected her repeatedly with a lower potency of fentanyl until she overdosed and died.”

The purity of the cartel’s fentanyl “varies greatly depending on the method and skill of the particular manufacturer,” prosecutors noted, and after a user overdosed on one batch, the Chapitos still shipped to the U.S.

When the elder Guzmán and fellow Sinaloa cartel leader Ismael “El Mayo” Zambada ran the gang, it operated with a certain degree of restraint. But with Guzmán serving a life sentence and Zambada believed to be suffering from health issues, the Chapitos moved in aggressively with unrestrained violence.

The arrest of Pérez Salas came just a few days after López Obrador met with President Joe Biden in San Francisco, continuing a trend of major arrests occurring days before or after meetings with Biden.

Ovidio Guzman López, one of the Chapitos, was arrested in January, just a few days before the two leaders met in Mexico City.

Ovidio Guzman was extradited to the United States in September to face drug trafficking, weapons and other charges. His father, El Chapo, is serving a life sentence in the U.S.

Vigil said of the timing of the arrests that “some of them are more than coincidence.”

“Andrés Manuel López Obrador may be trying to provide a gesture of goodwill in his final hours as president,” Vigil said. The Mexican president leaves office in September.

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