"Brother Wang was very important. He was number one," Enrique says, laughing knowingly.

Enrique—not his real name—describes himself as a high-level coordinator in Mexico's Sinaloa Cartel, one of the most powerful criminal organizations in the world.

On the outskirts of Culiacán, the capital of the state of Sinaloa, sitting in a car parked in a place where no one can hear him, he explains how the ingredients to manufacture the lethal fentanyl are transported from Chinese factories to laboratories in Mexico, traveling thousands of kilometers.

Members of his cartel credit “Brother Wang” with establishing this supply chain.

Known in the crime world as the “king of fentanyl,” Brother Wang is a 39-year-old Chinese national whose real name is Zhang Zhidong, according to the US Department of Justice. Arrested in Mexico in 2024, Zhang staged a spectacular escape before being recaptured and extradited to the United States in 2025.

Fentanyl is a synthetic opioid 50 times more powerful than heroin. It causes the death of tens of thousands of people each year, mainly in the United States, where the processed drug usually ends up. A dose as small as a few grains of salt can be lethal.

US President Donald Trump has described fentanyl traffickers as “narcoterrorists” and the drug and its components as weapons of mass destruction. Additionally, it has used the fentanyl trade as a reason to impose 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 most dangerous traffickers in the world.”

He also accused him of “running a global company that introduced massive quantities of cocaine, fentanyl and methamphetamine” into the United States and of laundering “millions of dollars from drug trafficking.”

Zhang has pleaded not guilty and is now awaiting trial. We contacted his attorney, who declined to comment while the case is ongoing.

Cartel members and former colleagues agreed to speak to the BBC to offer a rare insight into how they believe Zhang, a graduate of China's most prestigious university, allegedly became a key link in the chain between Chinese chemical manufacturers and Mexican pharmaceutical laboratories.

A “brilliant” student

Zhang graduated in 2010 from the prestigious Peking University, with a degree in Hispanic Philology, and a year later he traveled to Mexico to work for a Chinese-owned company dedicated to the extraction of iron ore. He soon landed a position of responsibility.

Those who knew him at that time saw him as a brilliant young professional, eager to live abroad.

“He was able to negotiate with people, very resourceful and able to adapt to all types of environments,” says Alex (not his real name), who studied at the same university and later worked in the same mining company as Zhang in Mexico.

According to him, Zhang spoke excellent Spanish, with an instinct for colloquial language and the ability to talk to anyone, always with a strong Beijing accent.

Alex says doing business in Mexico sometimes meant dealing with organized crime, including cartels, which control significant areas of the country. Zhang managed to establish relationships with “all the influential people there, both on the official side and the unofficial side,” Alex says.

According to Alex, Zhang loved this aspect of Mexico, describing him as a man attracted to risk and recklessness. He remembers Zhang crashing his boss's car without worrying about the consequences, and describes how one night he took him out of town to shoot road signs on a deserted highway with guns.

In 2013, the mining company went bankrupt and Alex returned to China, but Zhang stayed in Mexico.

Alex says that a year or two later, Zhang began posting in the Peking University Spanish alumni group on the WeChat platform, offering to exchange dollars at preferential exchange rates. Alex believes he was laundering money.

In addition, Enrique, a member of the cartel, claims that Zhang also became involved in drug trafficking. Court documents in the United States accuse Zhang of running “a large-scale drug trafficking and money laundering organization” since June 2016.

Enrique believes that Zhang began a romantic relationship with a relative of one of the cartel leaders and suggests that this helped him get closer to his inner circle.

The supply chain

Another cartel member who ran errands for the organization, Luis (not his real name), remembers a hot afternoon in 2019, when his bosses asked him to stand guard at a meeting where Zhang “came to offer his products.”

Luis claims that these products were the precursors—the basic chemical components—necessary to make fentanyl. He believes that Zhang was the one who, in effect, introduced him to the world of fentanyl and promoted this branch of the group's business.

Luis says that he soon became a “cook” of fentanyl, preparing the drug in a clandestine laboratory. He claims to have seen at least five other “cooks” die in front of him, and believes this was due to the substances they were handling leaking through the cracks in their protective clothing.

“Sometimes people just pass out and we have to get them out of the room,” he says.

Enrique describes how orders for precursors were placed with Zhang, who, he says, used his contacts in China to obtain the chemicals.

Also according to Enrique, the ingredients were then sent by air or sea to Mexico. He claims his own network would distribute them to fentanyl manufacturers, like Luis, in clandestine laboratories in Sinaloa.

When asked if he feels guilty for being involved in an industry that causes so many deaths, Enrique responds that one of his relatives died from a fentanyl overdose. “It stirs your conscience,” he says, but adds: “Work is work and we don't know any other way to make a living.”

When asked the same question, Luis said that he once tried to stop working in the laboratory, but his boss told him that the alternative was to go out and do surveillance rounds. He said that his boss gave him a choice: "You put on the vest, the equipment, and go out to fight; it's either that or you continue cooking."

According to Mexican security agencies, Zhang ran illegal operations spanning America, Europe, China and Japan.

Victoria Dittmar, a researcher at the InSight Crime think tank, has spent years investigating the flow of chemical precursors to Mexico. He claims that middlemen – the role Zhang is suggested to have played – are at the crucial intersection between chemical producers and cartels.

According to her, people with the reach that Zhang is said to have are “pretty unique” and “are key to the supply chain.”

“He was an intermediary that put Mexican drug trafficking organizations in contact with Chinese suppliers of chemical precursors,” a world that, according to her, is difficult to understand for those who do not belong to it.

“It also had a huge presence in the United States,” he adds. “You don't see that often… a person who can connect three regions.”

Mexican authorities claimed that Zhang was responsible for the export and distribution of more than 1,000 kg of cocaine, 1,800 kg of fentanyl and 600 kg of methamphetamine. They also accused him of handling more than $150 million in annual profits from drug trafficking.

The US Department of Justice issued a press release in 2025 with details of the indictment against Zhang. In addition to accusing him of drug trafficking, he claimed that he recruited people to open bank accounts in the names of more than 100 shell companies.

According to the document, they collected the money in various places in the United States, deposited it in the bank accounts of the shell company and transferred the funds to other beneficiary accounts to launder them outside the United States.

At the other end of Zhang's alleged operations is China. According to a 2025 US State Department report, the country is one of the world's leading producers and exporters of precursor chemicals used to make synthetic drugs.