Criminals that are making money from activities that are not legal will then want to cover up how they made that money. This is a process that is known as money laundering and there are many varieties of it that criminals will use in order to avoid being found out.
For example, it may be that a criminal organisation will open a shop or run a service to make it look as though they are making their money from that although this is really just a front for the activities that they are really hiding. Another common practice used by criminals in the past to do this was to open a casino.
In the modern world, the internet has provided criminals with the ability to do this anonymously, and this has meant that new laws have been put in place in many countries to crack down on this and make it much harder for criminals to be able to get away with it.
For example, nowadays when you go to the bank to open an account you will need to have a check like this done https://www.w2globaldata.com/regulatory-compliance-solutions-and-software/aml-id-checks/ called AML identity verification. This is to prove that you are who you say you are and it then means that police are more easily able to track down criminal activities.
Of course, there is still a lot of work to be done to prevent money laundering, and this is important for our communities and our safety, as well as for the economy.