Costa Rica's chief prosecutor says he'll investigate the political ties of a U.S.-wanted drug suspect photographed at President Laura Fernández's election victory party. Carlo Díaz announced the inquiry on Monday, October 5, targeting Guobin Tam Zhang, a China-born naturalised Costa Rican. Prosecutors will examine money laundering and possible illegal financing of the last election campaign.
Tam, also known as Juan Carlos Tam Cheong, faces extradition to the United States under a Florida federal indictment alleging drug trafficking and money laundering. Authorities arrested him on Friday, October 2, in Granadilla de Curridabat, an eastern suburb of San José.
The Prosecutor Moves on His Own
Díaz told La Nación he wouldn't wait for a complaint. "We are going to investigate any other background or relationship this person has at the political level," he said. Prosecutors first need a report from the party-finance department of the Supreme Electoral Tribunal (TSE), Costa Rica's election authority, he added.
With a judge's approval, investigators opened five devices seized from Tam, including four phones. Findings could lead to cases against other people, Díaz said. His office will suspend Tam's local cases to speed extradition, a step he described as usual practice. Front men, corrupt officials or party figures who knowingly accepted illegal money would still face investigation, he said.
Díaz heads the Public Prosecutor's Office and is seeking a second term. The Supreme Court will vote on that term on October 19. He called Tam one of the "invisible narcos," suspects without a visible criminal profile, and linked them to the second phase of his joint work with the DEA.
What the U.S. Case File Alleges
The U.S. and Costa Rican investigation began in October 2025 after a confidential source said Tam offered to launder money. An undercover agent later exchanged US$240,000 in Tether, a dollar-pegged cryptocurrency, for cash from him. Undercover buyers received about 6 kilograms of cocaine on January 15 and about 7 kilograms on February 16. Authorities seized both shipments. Agents told the courier the second load was bound for Florida. According to the case file, someone delivered US$100,000 in cash to a contact of Tam in Orlando on February 4. A second Costa Rican, Jeffry Oviedo Cerdas, is wanted in the same case.
Costa Rican prosecutors also link Tam to crime groups in Mexico and Colombia. CRHoy named the Sinaloa and Gulf cartels and Colombia's Clan del Golfo, which Washington has listed as Foreign Terrorist Organizations since 2025. On Monday, a San José criminal court ordered two months of provisional detention while the United States completes extradition papers. The Ministry of Justice and Peace placed Tam under a maximum-security regime.
Tam's lawyer, Moisés Chinchilla, said the political questions are "a separate matter that has nothing to do with the process."
Questions the Party Hasn't Answered
Tam appeared in photographs from the February 1 celebration at the Aurola hotel in San José. One photo shows him with Pilar Cisneros, a former lawmaker who now advises the presidency on communications without pay. Cisneros told La Nación the photo is genuine, but she has never spoken to Tam.
Fernández initially questioned whether the photo was real. "I do not know this person, I have not the slightest idea who he is," she said. She noted that about 2,000 people attended and that she couldn't know all of them.
Pueblo Soberano, led by party president and lawmaker Mayuli Ortega, rejected any suggestion of a financial relationship with Tam and offered to provide party records required by law. A certificate from the party's acting treasurer found no donations, contracts, transfers or contributions under three versions of Tam's name. But the party hasn't explained why he attended the celebration, Teletica reported. Ortega said the campaign team, not the party, organised such events.
The pressure isn't only coming from outside. Cisneros has said Ortega and party secretary general Freddy González should explain how Tam got into the event. Tam's former partner, Kathleen Quirós, a Legislative Assembly employee, challenged González in a video. "I am not going to say, like Freddy, that I did not know him; I knew him," she said, according to CRHoy.
What Remains Unknown
No extradition date has been set, and authorities haven't published the full U.S. charging document. The Prosecutor's Office is awaiting the election-finance report and hasn't said whom it will question. It's also unclear who invited Tam to the celebration. Tam hasn't been convicted, and no government official or party member has been charged with a crime.
The case comes as the government plans to open a new high-security prison for organised crime on Wednesday, October 14. Costa Rica extradited five men to the United States on October 1.
Why This Matters: Who gets into the room with a country's leaders is a question about democratic accountability, not just security. Díaz says he'll follow the money into campaign finance, and the TSE's report will show whether the system built to police party funding can do it. No official has been charged, and Tam hasn't been convicted. But the unanswered question of who invited him sits alongside a prosecutor who faces a Supreme Court vote on his own future on October 19. Whether an independent inquiry stays independent under that pressure is a test of Costa Rica's institutions, and the public has a stake in the answer.