Police busted a crime ring based in Spain that used credit cards and cryptocurrencies to launder €8mn ($9.8mn) from drug traffickers, Europol said on Monday.
The money launderers received the illicit proceeds from Colombian drug traffickers in cash. The cash was then divided up into small quantities and deposited into hundreds of bank accounts.
"As the cash was already circulating in the financial system, the ring just needed to transfer the criminal money back to the drug dealers in Colombia," a statement from EU law enforcement agency said.
"Once the criminals realised that cash withdrawals and bank operations were easy to track, they changed their laundering methods and turned to cryptocurrencies, mainly bitcoin," the Hague-based Europol explained.
Eleven people were arrested and 137 others are being investigated. The operations were led by Spain's Civil Guard with US and Finnish support.