Introduction
"Brother Wang was very important. He was number one,"says Enrique, chuckling knowingly.
Enrique – a pseudonym – identifies himself as a senior coordinator within Mexico's Sinaloa cartel, one of the globe's most influential criminal organizations.
On the outskirts of Culiacán, the capital city of Sinaloa state, Enrique, seated in a parked car to avoid being overheard, describes how precursors for manufacturing fentanyl are transported thousands of miles from Chinese factories to clandestine laboratories in Mexico. Cartel members attribute the establishment of this supply chain to Brother Wang.
Known in criminal circles as the "king of fentanyl," Brother Wang is a 39-year-old Chinese national named Zhang Zhidong, according to the US Department of Justice. Arrested in Mexico in 2024, Zhang escaped dramatically before being recaptured and extradited to the United States in 2025.
Fentanyl is a synthetic opioid approximately 50 times more potent than heroin. It causes tens of thousands of deaths annually, primarily in the US, where the finished product is frequently distributed. Even a dose as small as a few grains of salt can be fatal.
Former US President Donald Trump referred to fentanyl traffickers as "narco-terrorists," classified fentanyl and its precursors as weapons of mass destruction, and cited the fentanyl trade as justification for tariffs on China, Mexico, and Canada.
When Zhang appeared in a New York court in 2025, then-Deputy Attorney General Todd Blanche described him as one of "the world's most dangerous traffickers."
Blanche accused him of operating "a global enterprise that pumped massive quantities of cocaine, fentanyl, and methamphetamine" into the US and laundering "millions in narcotics proceeds."
Zhang has pleaded not guilty and is awaiting trial. His lawyer declined to comment due to the ongoing case.
Cartel members and former associates spoke to the BBC, providing rare insight into how Zhang—a graduate of China's top university—allegedly became a pivotal link between Chinese chemical manufacturers and Mexican drug laboratories.
Zhang the Man
Zhang graduated from Peking University in Beijing with a degree in Spanish in 2010. In 2011, he traveled to Mexico to work for a Chinese-owned iron ore mining company, quickly attaining a senior position.
Those acquainted with him then recall a bright young professional eager for international experience.
"He was capable of negotiating with people, very resourceful, and able to adapt to all kinds of environments,"says Alex, a pseudonym for a former colleague who also studied at Peking University and worked at the same mining company in Mexico.
Alex notes Zhang spoke excellent Spanish, including street vernacular, though with a strong Beijing accent.
Alex explains that conducting business in Mexico sometimes necessitated interactions with the underworld, including cartels that control large regions. Zhang reportedly established relationships with "whoever mattered locally—both the official side and the unofficial side."
Alex describes Zhang as attracted to risk and recklessness, recalling incidents such as crashing his boss's car without concern and taking Alex on a nighttime drive to shoot pistols at road signs on a deserted highway.
After the mining company collapsed in 2013, Alex returned to China, but Zhang remained in Mexico.
The BBC's investigation into Zhang Zhidong, identified by US law enforcement as a significant drug trafficker, reveals further details.
Alex states that one to two years later, Zhang began posting on Peking University’s Spanish alumni WeChat group, offering currency exchange at favorable rates, which Alex suspects was money laundering.
Additionally, cartel member Enrique asserts that Zhang became involved in drug trafficking. US court documents accuse Zhang of operating "a massive narcotics trafficking and money laundering organization" since June 2016.
Enrique believes Zhang entered a romantic relationship with a female relative of a cartel leader, facilitating his access to the cartel's inner circle.
The Supply Chain
Another cartel member, Luis (pseudonym), who performed errands for the organization, recalls a hot afternoon in 2019 when he was assigned to guard a meeting where Zhang "came to offer his products."
Luis states these products were precursor chemicals essential for fentanyl synthesis. He credits Zhang with introducing him to fentanyl production and initiating this segment of the cartel’s operations.
Luis became a fentanyl cook in a clandestine lab and witnessed at least five other cooks die due to chemical exposure through protective gear failures.
"Sometimes people just pass out, and we have to carry them out of the room,"he says.
Enrique describes placing orders for precursors through Zhang, who utilized his Chinese contacts to procure the chemicals.
The ingredients were shipped via air or sea to Mexico, where Enrique's network distributed them to fentanyl cooks like Luis in illicit Sinaloa laboratories.
When asked about guilt regarding the deadly impact of fentanyl, Enrique admits a relative died from an overdose, stating,
"It shakes your conscience,"but adds,
"work is work and we don't know another way to make a living."
Luis recounts attempting to leave the laboratory work, but his superior gave him a choice:
"You put on the vest, the gear, and you go out and fight - it's either that or working as a cook."
Mexican security agencies report Zhang managed illegal operations spanning the Americas, Europe, China, and Japan.
Victoria Dittmar, a researcher at the think tank InSight Crime, has extensively studied the flow of precursor chemicals into Mexico. She explains that brokers—roles attributed to Zhang—are critical intermediaries between chemical producers and cartels.
She describes individuals with Zhang’s reach as "quite unique" and "key to the supply chain."
"He was a broker that connected Mexican trafficking organisations with Chinese suppliers of precursor chemicals,"she says, noting the complexity of this world for outsiders.
"He also had a huge presence in the US,"Dittmar adds.
"You don't see that often… one person that can connect three regions."
Mexican authorities accuse Zhang of exporting and distributing over 1,000kg of cocaine, 1,800kg of fentanyl, and 600kg of methamphetamine, and handling more than $150 million in annual drug proceeds.
The US Department of Justice’s 2025 press release details Zhang’s indictment, accusing him of drug trafficking and recruiting individuals to open bank accounts for over 100 shell companies.
These accounts were used to deposit narcotics proceeds at various US locations and wire funds to beneficiary accounts abroad for laundering.
At the supply chain's origin is China, a leading producer and exporter of precursor chemicals for synthetic drugs, according to a 2025 US State Department report.
The report describes China’s chemical industry as "massive," comprising 160,000 companies. Despite government efforts to implement controls, oversight remains "insufficiently staffed and equipped."
The Chinese embassy in Washington told the BBC that China is "one of the world's toughest countries on counternarcotics."
It highlighted that China scheduled all fentanyl-related substances in 2019, imposing strict government controls. These substances are not banned due to legitimate industrial uses.
The embassy emphasized that China’s "extensive and in-depth" counternarcotics cooperation with the US has been "highly productive."
Escape and Arrest
Zhang’s alleged drug trade involvement ended abruptly with his arrest in Mexico on 31 October 2024.
A judge controversially placed him under house arrest, but Zhang escaped reportedly through a hole in a wall, fleeing by private jet to Cuba and subsequently to Russia.
Russian border officials detected forged documents, resulting in his return to Cuba, which extradited him back to Mexico. From there, he was sent to the United States.
Zhang’s arrest attracted global media attention. The Peking University alumni network was stunned.
"Everybody was talking about it,"says Alex.
"It was such a shocking story and he's probably one of the most famous people Peking University produced."
Cartel members in Culiacán report Zhang’s absence was immediately felt.
Luis states,
"It became really hard to get the precursors."
Enrique adds,
"They took the man and that caused a mess."He explains Zhang was "the one with the connections" in China, forcing cartels to "start from scratch and build a new route."
Concurrently, the US Drug Enforcement Administration noted a decline in fentanyl purity, consistent with difficulties faced by Mexico-based fentanyl producers in obtaining key precursors.
However, supply chain disruptions are typically temporary, part of a "constant game of cat and mouse," according to Dittmar.
Her research shows that when brokers are removed or chemicals controlled, fentanyl producers adapt by finding substitutes and new methods.
Individuals in the supply chain can also be replaced—even those with extensive connections like Zhang.
Enrique indicates a successor is emerging—another Chinese individual—but declines to provide details citing safety concerns.
Another cartel coordinator responsible for logistics states,
"Although all this started because of him [Brother Wang]… he left lots of connections to help us keep going."
"If he's gone, someone else will step in… the business will not stop."
Additional reporting by Ruth Evans and Miguel Angel Vega
