That is one strange bribe. If Spitzer was suspected of taking bribes it would be becuase he was depositing large sums of CASH into his bank account not withdrawing large sums of Cash.
That cannot be the reason.
Without knowing more details about the cash transfers, there are a couple of simple scenarios that make sense. They basically all revolve around transferring sums more than $10,000. Federal law requires that all transfers over $10K be sent to the Feds -- this was originally meant to catch drug dealers.
Meaning, all checks, wire transfers, credit card charges, etc., are sent to the Feds. My guess is that they look for repeated transfers and try and tie the transfers to legitimate business events -- paying a vendor, etc.
My guess is that Spitzer was moving hundreds of thousands per year. And this naturally stood out in the Fed's system, both because of the amount and his position.
The routine check revealed no business reason to transfer the money, nor gifts to children, relatives or charities, etc.
So if Spitzer was just moving his personal money to an offshore or blind account, and the Feds couldn't access where the money went after that, they would naturally assume that something was being covered up. Pretty simple.
Public servants shouldn't be shuffling money around unbeknownst to the public. It's the appearance of conflict which is the issue here. Also, their investments need to be placed in blind trusts so they can't be accused of profiting from decisions they make. This is standard practice now. Recognizing such, if a state Governor is moving money to invisible accounts then this would definitely merit an investigation, routine at first, to find out what's happening.
The theory could be that he was taking cash and depositing it into various accounts, then transferring the money to other accounts or persons.
Not TAKING bribes. GIVING.