Bank A writes a check to a customer. Customer takes the check to Bank B across the street and opens an account depositing the check of which the funds can't be touched until the check clears from Bank A.
Bank A clears the check to Bank B.
At no point is there an investigation as to how the funds were amassed, whether Bitcoin, drug sales, prostitution, payola for a murder contract, etc. The only concerns would be that funds are available from Bank A, and Bank B is happy to have you as a new customer.
You forgot one crucial step. If Bank A check is > "woah, that's a lot!" Bank B first contacts Bank A to ask why they want to move so much money out of their account. If Bank A tells them they closed the account because they had some issues or concerns, Bank B is not obligated to accept the check.
A few years ago I had a painful personal experience of trying to open an account with a $6,000,000,000 check from the Rothchild's, but no bank in the world wanted to touch it, despite lawyers flying around the world to meet the bankers personally, and as a result an immensely important project fell through once the check expired after a year.
LOL this story stinks to high heaven.
Want to see proof? I have the not-confidential-anymore signed and notarized document for the money transfer, and the business plan it was supposed to be used for.