Iran has found a new way to harm Americans and it’s not through bombs or guns.

For three years, Nemesis operated on the dark web, accessible only to those with specialized browsers designed to mask their identity and location. With 1,000 vendors selling narcotics, counterfeit identification documents, and hacking services, the site processed nearly $30 million in sales.

Nemesis had just one boss named Behrouz Parsarad. Working beyond the reach of American law enforcement in Iran, he designed the marketplace, controlled its operations, and handled all its finances. When international authorities finally seized Nemesis’ servers in March, more than 150,000 user accounts and over 1,100 seller accounts were reported to be registered on the site.

Particularly concerning to authorities was the selling of fentanyl, a synthetic opioid responsible for tens of thousands of American overdose deaths annually. According to data from the Centers for Disease Control and Prevention, there were an estimated 74,702 overdose deaths from the synthetic opioid last year. It’s considered to be 50 times stronger than heroin and 100 times stronger than morphine. Just 2 milligrams of fentanyl is considered a lethal dose.

Despite losing his marketplace, Parsarad hasn’t lost his criminal connections. Intelligence gathered in the weeks following the takedown shows the Iranian operator maintaining contact with his vendor network in an effort to relaunch. In response, Treasury officials moved on Wednesday to impose sanctions on his American assets including 49 cryptocurrency wallets.

“As the administrator of the Nemesis darknet marketplace, Parsarad sought to build—and continues to try to re-establish—a safe haven to facilitate the production, sale, and shipment of illegal narcotics like fentanyl and other synthetic opioids,” said Acting Under Secretary for Terrorism and Financial Intelligence Bradley T. Smith.

“Treasury, in partnership with U.S. law enforcement, will use all available tools to dismantle these darknet marketplaces and hold accountable the individuals who oversee them.”