By Vanessa BuschschlüterBBC News
EPAExtra security was deployed around the building to which "El Nini" was transferred in Mexico CityMexico's National Guard has arrested the alleged security chief of a faction of the Sinaloa cartel, Néstor Isidro Pérez Salas, also known as "El Nini".
"El Nini" is accused of leading a ruthless group of bodyguards providing protection for the sons of Joaquín "El Chapo" Guzmán.
The sons, known as "Chapitos" (little Chapos), rose to lead a faction of the cartel after their father was jailed.
The US had offered $3m (£2.4m) for information leading to his capture.
He is wanted there on drug trafficking and weapons charges.
DEAThere was a multi-million dollar reward for information leading to his captureThe US authorities are trying to stem the flow of fentanyl from Mexico to the US by targeting the cartels which are smuggling the synthetic opioid.
According to the US Drug Enforcement Administration (DEA), three of El Chapo's sons - Ovidio Guzmán López and his half brothers Iván Archivaldo and Jesús Alfredo Guzmán Salazar - have built a fentanyl-trafficking empire which smuggles millions of doses of the deadly opioid to the US.
Ovidio Guzmán López, also know as "El Ratón" (The Mouse), was extradited to the US in September and has pleaded not guilty to charges of drug trafficking and money laundering.
The two other "Chapitos" remain at large.
"El Nini" is suspected of leading a violent group which provides personal security for the brothers.
According to US investigators, "El Nini" is one of the most feared hitmen for the Chapitos, tasked with kidnapping, torturing and killing rival drug traffickers.
He was detained in Culiacán, the capital of the state of Sinaloa, which is the stronghold of the cartel of the same name.
In a joint operation, soldiers and members of the National Guard swooped down on the Colinas de Rivera neighbourhood.
Mexican media reported that "El Nini" tried to flee by climbing on to the rooftop of a house, but gave up after shots were fired.
He was quickly flown to Mexico City and extra security was deployed in Culiacán to prevent any outbreaks of violence such as those which paralysed the city after the first time Ovidio Guzmán López was arrested.
"El Nini" is thought to have been behind the group's retaliation for Ovidio Guzmán López's 2019 arrest, which included prison riots, shoot-outs and blockading major roads.
The violence was such that President Andrés Manuel López Obrador ordered Guzmán López be released.
Guzmán López was eventually re-arrested in 2023 and extradited to the US.
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