MakeIt,
As was mentioned earlier in this thread, Spitzer was making large wire transfers to shell companies operated by Emperor VIP's owners, and those transfers triggered automatic bank reporting requirements to the IRS, as there is a presumption that the money is income which someone is attempting to hide from the IRS. The IRS alerted the FBI, which began the investigation assuming Spitzer was being bribed and was funneling the bribe money into slush accounts. They then learned it was a private slush account set up to finance Spitzer's extremely expensive hobbying activities. Reports indicate that he was using Emperor VIP for many years.
Of course Spitzer as former Attorney General in New York should have known about these banking laws, and it is a major fucking mystery how he brain cramped on this one. I can tell you even with an attorney's private trust account (at least in Connecticut), banks are required to automatically report the attorney if the attorney's trust account is overdrawn by ONE FUCKING PENNY to the Statewide Grievance Committee that regulates attorneys. Those banking laws are designed to protect clients from having their money stolen from them by their attorneys. The banking laws that led to Spitzer getting investigated are designed to prevent the evading of reporting income to the IRS.
It's very ironic that they would have suspected Spitzer of taking bribes because his family is massively wealthy and it's almost certain he was using his own amassed wealth to fund his considerable and massively expensive hobbying activities. I have no doubt that Spitzer was spending 6 figures per year on escorts before he became Governor. It probably tapered some when he became Governor and was more regular when he was AG, due to the privacy/sneaking issues already mentioned above.