By Max Matza for BBC News
Undated images of Ismael "El Mayo" Zambada Garcia provided by the Mexican Attorney General's office in Mexico City on August 1, 2003. Photo: AFP / Mexican attorney general press office / Handout
One of the world's biggest drug lords, Ismael "El Mayo" Zambada, leader of Mexico's Sinaloa cartel, has been arrested by US federal agents in El Paso, Texas.
Zambada, 76, founded the crime syndicate with Joaquin "El Chapo" Guzman, who is currently jailed in the US.
Arrested with Zambada on Thursday was Guzman's son, Joaquin Guzman Lopez, said the US justice department.
In February, Zambada was charged by US prosecutors with a conspiracy to make and distribute fentanyl, a drug more powerful than heroin that has been blamed for the US opioid crisis.
In a written statement on Thursday evening, US Attorney General Merrick Garland noted that the two men lead "one of the most violent and powerful drug trafficking organisations in the world".
"El Mayo and Guzman Lopez join a growing list of Sinaloa Cartel leaders and associates who the Justice Department is holding accountable in the United States," Garland said.
American prosecutors say the Sinaloa cartel is the biggest supplier of drugs to the US.
The US Drug Enforcement Administration (DEA) had been offering a reward of up to $US15 million ($NZ25.4m) for Zambada's capture.
During Joaquin "El Chapo" Guzman's trial in 2019, his lawyers accused Zambada of bribing the "entire" Mexican government in exchange for living openly without fear of prosecution.
"In truth he controlled nothing," Guzman's lawyer, Jeffrey Lichtman, told jurors. "Mayo Zambada did."
According to the US State Department, Zambada is also the owner of several legitimate businesses in Mexico, including "a large milk company, a bus line, and a hotel", as well as real estate assets.
Alongside fentanyl charges, he is also facing charges in the US ranging from drug trafficking, murder, kidnapping, money laundering and organised crime.
"Fentanyl is the deadliest drug threat Americans have ever faced, and the Sinaloa cartel continues to be the largest trafficker of fentanyl into the United States," DEA administrator Anne Milgram said in a statement announcing the updated charges filed against him in February.
She also noted that fentanyl was the leading cause of death for Americans aged 18 to 45.
In May, Zambada's nephew - Eliseo Imperial Castro, who was known as "Cheyo Antrax" - who was also wanted on charges in the US, was killed in an ambush in Mexico.
This story was first published by the BBC.