To the best of my knowledge there are no Federal laws directly addressing prostitution. However, there are laws (the Mann Act) about transporting women across state lines for immoral purposes. I believe one could make a case for prosecution under this statute.

The other issue is the money transfers. Spitzer broke up his transfers into smaller sums to avoid triggering the automatic reporting to the Feds. If your intent is to avoid the reporting by breaking up the transfer this is called “structuring” and is illegal. He also asked the bank to keep his name off the transfers. This raised even more suspicions at the bank. The end results was the bank did report him to the Feds and the rest is history in the making.

I will grant you that consensual prostitution is a victim-less crime and shouldn’t be against the law. I will grant that transferring $10K or even $100K blocks of money around is no business of the Feds and they should not have the authority to snoop around in anyones financial records without a search warrant. But as someone in a position of power and trust he put himself in a position of being vulnerable to blackmail because what he did is against the law (and even if it was all legal he probably was vulnerable to blackmail with the threat of telling his wife). That shows exceedingly poor judgment and puts into question his fitness as a public servant. And at the very least it was required, for the good of the people of New York state, that all this be make public to eliminate the blackmail risk.

Bottom line: No conspiracy is required to justify the Feds actions.