Just the same as your local supermarket doesn't know if the $10 you gave them to buy a packet of cigarettes was obtained by murdering someone down the road and stealing it from the wallet in their lifeless body ... and then when the supermarket gives it to the next person who receives it as change, the shop that they take the $10 change to, to buy their grandmother flowers doesn't know that it is "tainted" money and will happily let you use it to buy the flowers ... then the child of the murdered person may get the $10 back as change when they buy flowers for the funeral of their parent ...
Lol I think this is more about counterfeit than it is about murder x.x