Over the past few years, New York State Attorney General Eliot Spitzer has been a master prosecutor, combining media savvy, damaging evidence, and hard-knuckle settlement negotiations.

That approach has worked well on Wall Street, with its keen understanding of economics: You pay some money to make a problem go away. Investment banks agreed to a $1.4 billion settlement regarding analyst conflicts. Mutual funds have paid $3 billion for late trading practices. Most recently, Marsh & McLennan (NYSE:MMC) paid $850 million over bid-rigging allegations.

Trials are time-consuming and tend to highlight problems. A settlement ends the negative buzz. Eventually, the public will forget about the problems, right?

Maybe. Maybe not. But there's an interesting counterpoint: Spitzer's recent cases involving white-collar crime have highlighted just how vague the law can be on such indiscretions, which makes successful prosecutions much more difficult.

Spitzer's first jury trial concerning financial fraud, which ended last week, was a clear defeat for the prosecutor. The jury acquitted defendant Theodore Sihpol on 29 of 33 charges, and declared a mistrial on the remaining four. Sihpol is a former broker at Bank of America, where he allegedly facilitated after-hours trades for the Canary Captial hedge fund and its managing principal Edward Stern.

It's interesting that Canary and Stern paid a $40 million fine to avoid a criminal trial. Herein lies an important question: Why not have Stern on trial? Wasn't he the one who orchestrated it all? Sihpol was a mid-level employee who apparently had his superiors' approval. Should Sihpol be the individual ultimately held responsible?

White-collar crimes are notoriously difficult to prosecute. The prosecution must not only prove guilt beyond a reasonable doubt, but also that there was intent to commit a crime. It's no easy task, especially in cases that involve complex business transactions. That appears to be the situation with the Sihpol trial; his attorney argued that there was no explicit law against late-day trading. How could Sihpol know he was doing something wrong?

Corporate America certainly seems to be gaining more protections. Even the U.S. Supreme Court is toughening standards for prosecuting white-collar crime. In the past few weeks, the court issued a rare unanimous decision to overturn Arthur Andersen's conviction for auditing fraud. The court's message was clear: The prosecution must show intent to commit a crime. True, Arthur Andersen is just one case, but every court decision is also a larger policy statement. The high court's Andersen decision could impact countless future decisions.

Spitzer has a variety of upcoming trials, such as the case against former New York Stock Exchange Chairman Dick Grasso. There is also a possibility of a criminal indictment against Hank Greenberg, the former CEO of AIG. But it seems that Spitzer's days of primarily positive headlines might be over. Now more than ever, the burden of proof falls on him.

Fool contributor Tom Taulli does not own any shares mentioned in this article.