So far, Spitzer, identified as "client 9" of an expensive Manhattan escort service by The New York Times (NYSE:NYT), faces no criminal charges. The New York Sun reported that prosecutors involved in the case are specialists in government corruption.

"I would expect prosecutors are looking quite broadly at the governor's use of money to see whether any public or campaign funds were involved," a former Justice Department official, Andrew Hruska, told the newspaper. "They would want to speak with all individuals whose names came up in the course of the analysis."

The Mann Act makes transporting prostitutes across state lines or persuading them to cross state lines a federal crime. The U.S. Supreme Court has ruled the law cannot be used to prosecute prostitutes.

In recent years, the law has been used only against human traffickers. The most famous person prosecuted under the act is probably Jack Johnson, the first black heavyweight champion. He was imprisoned for sending his white girlfriend a train ticket.