Europol has shut down a drug trafficking ring that used cryptocurrencies and credit cards to launder more than €8 million through a Finnish crypto exchange.

Announced Monday, Europol arrested 11 individuals for laundering funds from Spain to Colombia through an unnamed cryptocurrency and credit cards, according to a statement. Spain’s Guardia Civil, Finnish law enforcement authorities and the investigative arm of the U.S. Department of Homeland Security helped execute the arrests.

Roughly 137 individuals were investigated, and the suspects used a total of 174 bank accounts, according to the statement, which continued:

“The criminals based in Spain were contacted by drug traffickers to launder money obtained from their illegal activities. They picked up the illicit proceeds in cash, which were then split into small quantities to be deposited into hundreds of third bank accounts.”

With the cash “circulating in the financial system” the alleged criminals first used credit cards to withdraw the money in Colombia, but fearing discovery, they subsequently shifted to converting the funds into cryptocurrency and then into Colombian pesos through the Finnish crypto exchange.

Europol’s statement noted that the unnamed exchange cooperated with Finnish authorities by sharing the suspects’ information.

The EU law enforcement agency said it plans to strengthen its efforts to police criminal activities carried out with cryptocurrencies.

“Europol will continue to coordinate across EU Member States and beyond, to effectively respond to this rising threat,” its statement read, adding that it has implemented “specialized training courses to assist law enforcement officers in identifying the use of cryptocurrencies by organized crime networks.”

Europol has previously issued reports on the illicit usage of cryptocurrencies, most recently warning that zcash, monero and ether are increasingly implicated in cybercrimes in addition to bitcoin.

Spanish patrol car image via Shutterstock