Rob Wainwright, the head of the European Union's police service called Europol, described the 3-4 billion pounds that criminals hide in crypto-currencies. It's just about money in Europe. This is reported by CBR Online.
It’s growing quite quickly and we’re quite concerned. They’re not banks and governed by a central authority so the police cannot monitor those transactions. And if they do identify them as criminal they have no way to freeze the assets unlike in the regular banking system.
According to Wainright, the problem is becoming more widespread. Banks and governments can not control the conducted transactions crypto-currency, therefore it is difficult to track funds. Large amounts of tokens are broken into small ones, they are sent to different purses, and it is extremely difficult to track the origin of the funds.