Americans were fascinated as they tuned in by the millions to the daily televised coverage. But viewers overseas were often confused. The answers to these questions lie in the complex nature of the U.S. judicial system and its parallel system of federal and state courts. The U.S. Constitution assigns specific powers, including certain law-making powers, to the federal government, reserving all other powers to the states. Accordingly, there are federal courts for prosecution of violations of federal law, and state courts for violations of state law.
Most crimes are violations of state law.
Even the serious crime of murder, in most cases, is a violation of state law in the United States. That is why O.J. Simpson was prosecuted by the state of California, where the crime occurred, and not in the federal courts. Simpson was not required to testify at his murder trial because he had the constitutional right not to, unless he so chose. In fact, defendants in the United States have a myriad of rights that emanate from the Constitution itself, whether or not they are prosecuted in state or federal court. Simpson would have had the same right not to testify against himself in a federal criminal trial, for example.