When Tigran Gambaryan was first invited in February to meet with the Nigerian government in order to settle a dispute with his employer, the cryptocurrency exchange Binance, Nigerian officials detained him against his will, stripped him of his passport, and told him he was a “guest” of the state. He’s since been charged with financial crimes and jailed for months as a criminal suspect.

Pressure is now mounting within the US Congress for the Biden administration to treat him as what his supporters argue he has been all along: a hostage, held illegally by an unaccountable foreign country.

On Wednesday, US congressman Rich McCormick, who represents Gambaryan’s district in his home state of Georgia, submitted a resolution to the House Committee on Foreign Affairs that both urges the Nigerian government to release Gambaryan and calls on the US government to recognize that Gambaryan is being illegally detained as a hostage in an effort to extort his employer, Binance. That resolution represents the latest in a series of growing calls from Congress for the White House to step up its pressure on Nigeria to release Gambaryan, a former federal agent who led many of the most significant cryptocurrency-related criminal cases of the last decade during his time as an IRS criminal investigator.

“The continued detention of Tigran Gambaryan in Nigeria is a clear violation of his rights, and he is simply being used as a means of extortion by the Nigerian government,” McCormick wrote in a statement. “We urge Nigeria to immediately release Tigran and provide him with the necessary medical care and due process. The United States Government must do everything in its power to secure the release of Tigran Gambaryan, and all of our citizens wrongfully detained abroad.”

McCormick’s resolution to push for Gambaryan’s release follows an earlier open letter from 16 members of Congress calling on the White House to transfer Gambaryan’s case to the Office of the Special Presidential Envoy for Hostage affairs. That letter noted that Gambaryan has suffered from malaria and pneumonia, collapsing in court during one day of his trial, yet has been denied proper care in a hospital. “Gambaryan’s health and wellbeing are in danger, and we fear for his life,” the letter read. “Immediate action is essential to ensure his safety and preserve his life. We must act swiftly before it is too late.” Two House members, French Hill and Chrissy Houlahan, visited Gambaryan in jail last month and have also called for his release.

Gambaryan and another Binance staffer, Nadeem Anjarwalla, flew to Abuja in late February at the invitation of the Nigerian government after the country’s officials accused Binance, where Gambaryan works as head of its investigations and financial crime compliance, of money laundering and contributing to the devaluation of the country’s national currency, the naira. But just days into that negotiation, the two men were detained in a government-run “guest house” against their will.

The situation escalated further when Anjarwalla, who is based in Kenya, escaped during a visit to a mosque for Ramadan prayers. Gambaryan was then criminally charged with tax evasion and money laundering—all signs suggest those charges relate to the behavior of Binance, not Gambaryan personally—and moved to Kuje prison, where he has since been held.

Tigran Gambaryan

Tigran Gambaryan

Photograph: Binance

The charges against Gambaryan are particularly ironic given his track record as a federal agent. Prior to being hired by Binance, which was widely seen as part of the exchange’s efforts to clean up its operations’ lax compliance and years of alleged money laundering documented in a $4.3 billion settlement with the US government last year, Gambaryan spent a decade leading many of the most significant crypto crime investigations in history. From 2014 to 2017 alone, for instance, Gambaryan identified two corrupt federal agents who had enriched themselves with cryptocurrency from the Silk Road dark-web drug market, helped to track down half a billion dollars worth of bitcoins stolen from early crypto exchange Mt. Gox, helped develop a secret crypto tracing method that located the server hosting the massive AlphaBay dark web crime market, and helped to achieve the takedown of the Welcome to Video crypto-funded child sexual abuse video network.

Gambaryan’s supporters point out that his work for the IRS led to the seizure of more than $4 billion dollars, including several of the largest monetary seizures in the history of US criminal justice. “He’s done so much good for this country throughout his career,” Gambaryan’s wife Yuki told WIRED in March. “I believe it’s his turn to get the same amount of support from his country.”