As a propeller plane on Thursday whirred towards the U.S.-Mexico border to cross illegally, U.S. agents raced to meet it at a small municipal airport near El Paso, Texas, and arrest two men who were part of Mexican drug trafficking royalty.

The son of jailed former Sinaloa Cartel kingpin Joaquin "El Chapo" Guzman planned to give himself up upon landing. The other passenger - legendary septuagenarian trafficker Ismael "El Mayo" Zambada – did not and was duped into getting on the plane by the younger man, according to two current and two former U.S. officials familiar with the situation.

Zambada's arrest followed lengthy surrender talks between U.S. authorities and El Chapo's son, Joaquin Guzman Lopez, the sources said. But many American officials had given up hope on Joaquin turning himself in, and were caught unaware when he sent a last-minute message that he would arrive with a kingpin U.S. authorities had been chasing for four decades.

"El Mayo was the cherry on top," said one U.S. official, who declined to be identified because he was not authorized to speak publicly about the arrests. "It wasn't expected at all."

Guzman Lopez had convinced Zambada to board the plane by telling him that they were flying to see real estate in northern Mexico, according to the two current and one former U.S. officials.

Reuters was the first news organization to report the arrests, ahead of a Department of Justice statement on Thursday evening that confirmed the two men had been detained in El Paso. The news agency spoke to current and former officials to piece together a detailed account of the operation.

The U.S. Federal Bureau of Investigation (FBI) and the Homeland Security Investigations (HSI), the two agencies who carried out the operation, scrambled agents from their local El Paso offices and barely reached the airport by the time the private plane was landing, according to a fifth source, a U.S. official who declined to give further details on the arrests.

One worker at the Dona Ana County International Jetport, near El Paso, told Reuters he saw a Beechcraft King Air plane land on Thursday afternoon on the runway, where federal agents were already waiting.

"Two individuals got off the plane ... and were calmly taken into custody," said the man, who declined to share his name out of concern for his safety.

The unexpected arrest of El Mayo, in his late 70s, and the way he appears to have been betrayed by Guzman Lopez, who is about 38 years old, has jolted the Mexican drug trafficking world, triggering fears of a bloody fissure in the Sinaloa Cartel between the two families that control the group's biggest power bases.

Zambada is accused of being one of the most consequential traffickers in Mexico's history, having co-founded the Sinaloa Cartel with "El Chapo" Guzman, who was extradited to the U.S. in 2017 and is serving a life sentence in a maximum security prison in Colorado.

Reuters could not determine why Guzman Lopez betrayed his father's long-time partner, though the four current and former sources said it was likely due to his desire to obtain a more favourable plea bargain deal from U.S. authorities and help his brother, Ovidio, who was arrested and extradited to the United States in 2023.

U.S. authorities have made drug bosses key targets, frequently striking plea bargain deals with them in exchange for information that leads to the capture of other high-ranking cartel figures.

The back-channel communication between American officials and Guzman Lopez was carried out through lawyers, the first official said. Jeffrey Lichtman, who represents both Guzman brothers, declined to comment.

Zambada, who was in a wheelchair, pleaded not guilty on Friday in a Texas courtroom to drug charges, including continuing criminal enterprise, narcotics importation conspiracy and money laundering.

His lawyer, Frank Perez, said on Friday that Zambada did not come to the U.S. voluntarily. On Saturday night, Perez said Guzman Lopez had "forcibly kidnapped" in Mexico and brought him to the United States against his will.

Guzman Lopez is due to appear in court next week in Chicago, where he was first indicted on drugs charges around 6 years ago.

Guzman Lopez is one of four sons of El Chapo - known as Los Chapitos, or Little Chapos - who inherited their father's faction of the cartel. Joaquin and Ovidio have the same mother, while the other two siblings – Ivan and Jesus Alfredo – hail from El Chapo's first marriage.

The brothers have in recent years come under ferocious pressure from U.S. authorities, who have made them their main anti-narcotics targets, portraying them and the Sinaloa Cartel as the biggest traffickers of fentanyl into the United States. Fentanyl overdoses have surged to become the leading cause of death for Americans between the ages of 18 and 45.

Ray Donovan, a former high-ranking U.S. Drug Enforcement Administration (DEA) official, said the defeats suffered by key Sinaloa Cartel bosses in the recent past are mainly down to their embrace of fentanyl, which has risen up the political agenda in Washington as the death told has mounted on U.S. streets.

"The number of Americans dying has put a lot more pressure," Donovan said. "Fentanyl brought them down."

On Friday, U.S. President Joe Biden heralded the arrests and vowed to continue combating "the scourge of fentanyl".

NEW GENERATION OF NARCOS

El Chapo's sons are known to be more violent and hot-headed than Zambada, who had a reputation as a shrewd operator that liked to stay in the shadows. Guzman Lopez was also seen as less important than his other three brothers.

The U.S. authorities had a $15 million reward for the capture of Zambada, who co-founded the Sinaloa Cartel in the late 1980s with El Chapo. Guzman Lopez had a $5 million bounty on his head. Both men face multiple indictments in the United States.

The first U.S. official cautioned that there are still many questions unanswered about how or why Zambada, an ultra-cautious and experienced cartel chieftain, found himself on that plane.

Mexican Security Minister Rosa Rodriguez said that Mexico was informed of the detentions by the U.S. government, but that Mexican authorities did not participate in the operation.

Outgoing Mexican President Andres Manuel Lopez Obrador has taken a cautious approach to tackling the powerful cartels, curbing security cooperation with U.S. authorities on fears that the previous U.S.-Mexico strategy of targeting powerful kingpins was triggering more nationwide violence.

In Oct. 2019, Mexico's military arrested Ovidio but were forced to release him after hundreds of Sinaloa Cartel foot soldiers blocked roads and fought running gun battles with soldiers as they to lay siege to the city of Culiacan, the capital of Sinaloa. The military arrested Ovidio again in Jan. 2023 and he was extradited in September last year.

Matthew Allen, a former Special Agent in Charge of HSI's Arizona division that built indictments against Guzman Lopez and other Sinaloa Cartel figures, said both Zambada and Guzman Lopez had had periodic conversations with U.S. officials about surrendering over the years.

Allen, who maintains regular contact with former colleagues at HSI, said many traffickers, especially those from the younger generation, realize that giving themselves up, serving some time in jail and then spending their wealth is a better option than risking death from rivals in Mexico or capture by authorities that can lead to lifelong prison terms. Some informants are allowed to enter witness protection programs.

"They're seeing that this way you can do your time and do not have to look over your shoulder for the rest of your life," he said.