Brian Ross at ABC News reports that the underlying crime here might not be related to prostitution:
The federal investigation of a New York prostitution ring was triggered by Gov. Eliot Spitzer’s suspicious money transfers, initially leading agents to believe Spitzer was hiding bribes, according to federal officials.
It was only months later that the IRS and the FBI determined that Spitzer wasn’t hiding bribes but payments to a company called QAT, what prosecutors say is a prostitution operation operating under the name of the Emperors Club. […]
Spitzer, who made his name by bringing high-profile cases against many of New York’s financial giants, is likely to be prosecuted under a relatively obscure statute called “structuring,” according to a Justice Department official.
Structuring involves creating a series of financial movements designed to obscure the true purpose of the payments.