According to this abcnews story, Spitzer’s involvement with this ring was not uncovered by virtue of some happenstance over-hear on a wiretap involving a prostitution ring. Rather, the feds targeted Spitzer himself based on a suspicious activity report filed by his bank, which noticed him paying large amounts of money in ways that it thought were evidence of criminal conduct. This report says Spitzer is suspected of “structuring” which is the intentional structuring of financial transactions involving cash in amounts less than $10,000 for the purpose of avoiding the filing of “Currency Transaction Reports” with IRS and FBI. They indicted the prostitution ring based on what they uncovered in looking into Spitzer, but the facts suggest to me that Spitzer has received a target letter indicating that he is the target of a federal criminal investigation for his conduct.