The theory could be that he was taking cash and depositing it into various accounts, then transferring the money to other accounts or persons.
That is not probable cause of anything and certainly not illegal.
No part of that in itself is illegal! I have done it lots of times. For example If I am buying something and the seller wants the money in an account so he knows I have it. I don't want to give him the right to examine one of my main bank accounts so I transfer just the funds required to a new bank account and give him access to look at the contents of the account at any time up to the closing. I could open an escrow account but this is often easier to do. Some sellers demand an escrow account. But that is still a transfer of funds.
I once sold my stock in radio station of which I was President, and its major stock holder. I sold it to a minority stock holder. I was to receive all the savings account deposits of the corporation as well as cash for my stock.. So I closed the corporate savings accounts and then transfered that money to one of my personal accounts at closing.
The buyer then paid me for my stock and I transfered that to another personal account. Then I transfered both sums in these personal accounts to two personal money market accounts. And then transfered one of these accounts, less taxes, to my stockbrokers account which he used to to buy assorted stocks in my name. The banks I am sure reported the transactions, but nothing I did was even close to being illegal. It was totally legal.
They would have to have probable cause that the transaction was likely to be illegal and then get a judge to so rule. Just the act of a transfer to cash or to other accounts is never enough to do anything. He could have just been hiding the cash in his mattress. Getting cash and transferring it through a hundred other accounts is not by itself illegal. And if that is all they have, getting a court order to examine account details or look deeper is not going to be granted. If all the law has is money transfered from account to account,that will not get a court order to examine the accounts or much of anything else.
There is no real way to really follow cash once it is withdrawn. And withdrawing cash is not illegal. Some auctions especially car auctions require cash, certified checks, or casheirs Checks for purchases. Dealers and collector's don't know what price they will be paying at auction so the payments are often made partly with certified checks and the remainder with cash. Collectors may quite often pay the entire price with cash.
That is not illegal either. If a dealer is going to several auctions to buy lots cars he may have withdrawn a lot of cash. That is not illegal either.
Some businesses traditionlly operate with cash. Grocery stores pay nearly every thing with cash. Every individual owned grocery store that bought radio time from one of my radio stations always paid in cash.
It is not at all unusual for an small grocery store or carryout to withdraw thousands of dollars every week to pay for new stock.
The law has to have probable cause that the person is doing something illegal before they can take action to get wire taps and other ways of investigating.
If the congress will not give Bush the right to wire tap a suspected terrorists with out a court order, what do you think the chances are on getting a wire tap on the Governor of New York without probable cause.
It does not happen.