Even if hackers managed to steal billions of usd worth of bitcoin and found a buyer such as a corrupt finance institution in some third world country and got paid fiat (cash) by the corrupt finance institution, how could police trace the bitcoin back to them if the buyer took control of all their previous owner bitcoin? i.e. corrupt banking official working with corrupt government officials acquiring the bitcoin from the hacker? What if the hacker used most of the bitcoin to buy a five star hotel in some third world country but under "different ownership"?