to check every deposit to see if the money is legitimate. The banks and the governments have to assume the money is legitimate, and allow people to deposit. However, if there is a probable cause, the banks and the government have good reason to doubt the src of the money, they have the right to freeze it and let the account holders to provide evidence to prove otherwise. This is how to protect personal properties. Otherwise, any criminal can seizes other peoples' assets and claim to be their own, and no one can touch them.