PANAMA CITY — On the 21st floor of a gleaming skyscraper in the heart of the upscale Punta Pacifica neighborhood here is the official corporate office of Polymarket, the wildly popular prediction market site that has flourished in President Trump's second term.

Polymarket, which is worth an estimated $15 billion, moved to its Panama base following scrutiny from American regulators. If Polymarket users have a legal dispute, the company's terms of service states it will be resolved in a closed-door arbitration process in Panama.

But when NPR recently visited the law office listed as its home base in Panamanian government documents, there was no sign of Polymarket, nor the entity it does business as in Panama, Adventure One QSS Inc.

Instead, a nondescript corporate lobby opened into a large space with about a dozen unoccupied computer stations positioned in the middle of the room. An office worker said the attorney who runs the firm, Mario García de Paredes, was not available. The worker had never heard of Polymarket or Adventure One.

Public records show that Polymarket is far from alone in using this Panama City law office as a headquarters in an office park known as the Oceania Business Plaza. So do at least 15 other cryptocurrency companies, including Helix, Drift Protocol, Goldfinch and Parti, a crypto-based prediction market live-streaming site that partners with Polymarket, according to publicly available corporate records.

Court filings show the law office also did work for FTX, the now-collapsed exchange whose founder, Sam Bankman-Fried, was handed a 25-year prison sentence in the fraud scandal that took down the crypto empire. In a bankruptcy document detailing unpaid FTX debts, the law office is listed as being owed $13,889.

Polymarket and the other companies using the Panamanian law firm did not return requests for comment. Neither did García de Paredes when asked repeatedly for comment by NPR.

Corporate law experts say while there is nothing illegal about housing a business inside a shell company, the practice is often a strategic move to protect a firm's wealth or shield it against lawsuits and action from government regulators.

"From a tax and regulatory point of view, Panama offers many advantages," said Bruce Zagaris, a Washington lawyer who specializes in international criminal law.

After the Biden administration cracked down on Polymarket for operating without a license in 2022, it wound down its U.S. business and set up shop in Panama, a country that has long been a popular tax haven for American firms looking for an off-shore subsidiary.

Billions of dollars are traded every week on Polymarket's overseas exchange, including bets on war, military strikes and the toppling of world leaders, which are illegal under U.S. commodities law.

From FBI raid to explosive growth

The prediction market industry has seen breathtaking growth in President Trump's second term.

On Polymarket, more than $8 billion was traded in April alone, compared to less than $1 billion last April, according to analytics firm The Block, which estimates that, together with Polymarket's main competitor, Kalshi, the prediction market industry recorded more than $24 billion in trades last month.

It's a remarkable reversal of fortunes for Polymarket.

Under a 2022 settlement hammered out with the regulators in Washington, Polymarket had to pay a $1.4 million fine and shutter its American business in the U.S. for operating as an unlicensed exchange.

Two years later, FBI agents used a battering ram to break down the door of Polymarket CEO Shayne Coplan's Manhattan apartment as part of a probe into whether Polymarket was violating that settlement.

Within months of Trump's second inauguration, those problems started getting smoothed out.

The Justice Department dropped its investigation into Polymarket. Donald Trump Jr., the president's son, became an adviser to the company and his venture capital firm, 1789 Capital, invested millions into Polymarket. Trump's regulators approved a deal allowing a separate version of Polymarket to re-enter the U.S. Administration officials invited Coplan to the White House for a roundtable on cryptocurrency.

Meanwhile, the website where all of Polymarket's action happens remains technically banned in the U.S. under the 2022 settlement.

It's an awkward position for the company: the Trump administration has openly embraced it, even as the billions of dollars in bets flowing on the site weekly are not supposed to be available to Americans.

Polymarket trades, whether on the likelihood of a nuclear detonation, how far a California wildfire will spread, or when the U.S. will strike Iran, are accessible in "view-only mode," meaning it's possible to see how people are betting, but U.S.-based traders are prevented from putting any money down.

Polymarket's terms of service tell users not to use a virtual private network, known as a VPN, which can disguise where exactly someone is connecting from online.

Timothy Massad, the former chairman of the Commodity Futures Trading Commission, which oversees U.S.-based prediction markets, said there are real questions about what exactly Polymarket is doing to prevent American users from accessing its overseas exchange.

"They could certainly require stronger geofencing so it becomes even more difficult for U.S. users to participate," he said, referencing the tactics used to block people from a certain region from accessing a site.

Some geofencing approaches, for instance, require that users verify their physical location using GPS to ensure someone is not just appearing to be in another location with a VPN.

As an indictment last month against a soldier accused of netting more than $400,000 on military secrets shows, Polymarket's rules against VPNs can be bent.

Prosecutors allege the U.S. Army master sergeant, Gannon Van Dyke, committed wire fraud and other crimes when he masked his location in North Carolina with a VPN, allowing him to wager $33,000 that Venezuelan leader Nicolás Maduro was on the verge of being taken out of power. Van Dyke would know, authorities said, since he was directly involved with planning and carrying out the operation. Van Dyke has pleaded not guilty to the charges.

Polymarket's Coplan thanked the Justice Department for acknowledging Polymarket's cooperation in the investigation in a post that seemed to convey just how much scrutiny his site is under these days.

"Noise aside, the reality is we work proactively with all relevant authorities on any suspicious activity on our marketplace," Coplan wrote on X. "This happens constantly behind the scenes, despite what many are led to believe."

Some are led to believe otherwise, in part, because of Polymarket's corporate shield in Panama.

The Panama advantage: Tax-free with legal perks 

A decade ago, the Panama Papers, an international investigative reporting project, illuminated how the ultra-rich conceal their wealth in off-shore tax havens, like the British Virgin Islands, the Bahamas and Panama.

Polymarket has long had an office in New York City's Upper East Side and has never misrepresented its presence in Panama, where the company does not have any employees.

Still, in response to NPR's questions, Polymarket would not specify why it chose Panama as its legal residence.

Lawyers who help American companies set up Panamanian subsidiaries pointed to the benefits cited most frequently by U.S. firms.

First, the tax benefits: There's no income tax for Panama-based companies whose work happens outside the country. There is also no capital gains tax on investments.

Another big advantage to locating in Panama is legal: It can be a reprieve from civil judgements from foreign courts.

"It's a long legal process. There are a lot of formalities and hoops to jump through," said David Mizrachi, a lawyer with a private practice in Panama.

An attorney who has helped crypto startups establish corporate roots in Panama, including in the same building Polymarket uses, said there is an "innocuous layer" to going to Panama, comparing how many American firms incorporate in Delaware and are not based there.

But when Panama serves as a company's official headquarters, it can provide a legal shield. "Companies are always seeking protection from civil and criminal risk, and Panama can offer that," the lawyer said.

"If you're someone trying to enforce a judgement, good luck getting a Panamanian court to do that," said the lawyer, who was not authorized to speak publicly about the work.

For instance, Panamanian law views judgements from foreign courts as presumptively invalid, unless the country's supreme court approves them, Mizrachi noted.

Zagaris, the international criminal law expert, said Polymarket's Panama base gives Trump officials a justification for taking a mostly hands-off approach, since all the controversial betting on the site is outside the jurisdiction of regulators in Washington.

Nonetheless, that posture could change when Trump is out of office.

"Offshore platforms still have a responsibility to determine where their customers come from," Zagaris said. "If you don't have law enforcement difficulties with this administration, they might have them in the next."

Eliana Morales Gil reported from Panama City