Police in Greece have arrested a man wanted in the United States for allegedly running a massive Bitcoin-based money laundering operation, according to the Associated Press. Authorities say the 38-year-old Russian man was responsible for converting $4 billion in illicit, conventional cash into virtual currency.

The suspect hasn't been publicly named, but Reuters got a picture of him being arrested. According to Reuters, he was arrested in the "Greek region of Chalkidiki on Monday on a US warrant."

The news is a reminder that—like ordinary cash—Bitcoin has a wide variety of uses, both legitimate and illicit. Bitcoin boosters like to focus on potential applications like international remittances, micropayments, and conventional retail sales. But Bitcoin has become the payment network of choice for "dark Web" markets for drugs and other illicit merchandise, from the original Silk Road—shut down in 2014—to the recently busted AlphaBay.

Conventional financial institutions comply with anti-money laundering regulations that make it difficult for criminal organizations to use their payment infrastructure. Networks like MasterCard and Visa blacklist suspected criminal enterprises as soon as they're identified. So criminals are always on the lookout for alternative payment systems that are not as strictly regulated. And Bitcoin's decentralized architecture, which puts it beyond the control of any government or financial institution, makes it an attractive option.

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