John Cassese is fighting for his freedom. His future depends on a deceptively simple question: What is a crime?

Is accidentally bumping into someone on the sidewalk an assault? What about unintentionally rear-ending another car on the expressway? If you flub the math on your tax return, are you guilty of criminal tax evasion? What if your backyard barbecue ignites your neighbor's garage -- is that arson?

The very definition of a "crime" hinges on two things: a criminal act and a criminal mind (wrongful intent). The prosecutor's job is to prove both the wrongful act and the wrongful intent beyond a reasonable doubt.

This two-part definition provides a basic -- and critical -- protection of civil liberties. The requirement that there be a criminal act assures that no one goes to jail for a "thought crime." Just as important, the intent requirement means people can't be tossed in the slammer for making a mistake. Bumping into someone, rear-ending a car, forgetting to carry the "1" on your taxes -- if done inadvertently, none of these things is a crime.

For crimes like murder or theft, the intent requirement still rules. But when it comes to "white collar" offenses, lawmakers, prosecutors, and others who want speedier (and easier) convictions are weakening this vital protection. Just ask Cassese, a New Jersey businessman.

Cassese founded Computer Horizons in 1969 and, over the next 30 years, helped build it into an international leader in information technology services. In April 1999, Cassese considered merging his business with a similar company called Compuware. But brief negotiations were unsuccessful. Eventually, Compuware's CEO called Cassese to tell him they had decided to merge with another company, DPRC.

Assuming the merger -- like the one he had discussed with Compuware -- would be handled privately, Cassese promptly purchased 15,000 shares of DPRC. Nothing wrong with that. It's perfectly legal to buy stock, even with private information about a merger, as long as the merger does not involve a tender offer (a public offer to purchase stock for more than the going price) and the buyer does not work for one of the companies involved.

The brokers involved in the purchase later testified that these trades were typical. There was no indication Cassese was trying to hide anything. He did nothing out of the ordinary.

Only when Compuware publicly announced its acquisition of DPRC, did Cassese learn the deal involved a tender offer. When his broker reached him with the news, Cassese sold all the stock. He made about $150,000. He later asked if it was possible to cancel the trades, but they could not be undone.

Two and a half years later, the government sued Cassese, alleging insider trading in DPRC stock. In civil court, the government can sue even for an accidental violation of securities law -- there is no requirement to show criminal intent. Cassese settled immediately, giving up all his profits plus a large penalty -- $321,387.84 in all.

When asked about the settlement, Cassese told the Bergen Record, "I never tried to hide anything. If I made a mistake, I made a mistake."

The matter appeared settled. That is, until political pressure to throw most any "suit" into the slammer apparently convinced prosecutors that Cassese should pay even larger fines and go to prison -- up to 10 years for each of two criminal charges.

A judge in the U.S. District Court for the Southern District of New York threw out one frivolous charge right away. A jury found Cassese guilty of the second charge, but the judge threw out that conviction, too. There were simply no facts, the judge said, that showed Cassese intended to break any law.

Without knowing that the merger was a tender offer, Cassese had no reason to think that his actions were illegal. He had no criminal intent. It seems a most reasonable ruling, but prosecutors are contesting it in the U.S. Court of Appeals for the Second Circuit.

That's worrisome for Cassese, and dangerous for all of us. We all make mistakes. If prosecutors are given a pass on proving criminal intent, every one of us could be branded a criminal.

In 1998, the American Bar Association reported that Congress had created more than 3,300 separate criminal offenses. A new report estimates that today there are more than 4,000 federal crimes. This push to criminalize just about everything endangers everyone if we snare the unsuspecting as well as the criminally minded.

Criminal justice is not about punishing the mistaken; it's about punishing those who choose to commit criminal acts. The requirement that government prove criminal intent to gain a criminal conviction is fundamental to the protection of freedom and civil rights. To gut it would be a crime.

Trent England is a legal policy analyst at The Heritage Foundation's Center for Legal and Judicial Studies and the editor of www.overcriminalized.com.