There are two main bodies of law in the United States, federal law and state law. Most crimes committed in the United States fall under one or more state laws and, as such, are heard in a state criminal court. Some acts, however, constitute violations of federal law for which the alleged perpetrator must appear before a federal court to plead his or her case.
Federal criminal cases are normally investigated by one or more federal agencies such as the DEA, FBI, and the ATF, among others. Before charges are filed, evidence is brought before a grand jury. A U.S. attorney acts on behalf of the United States as the prosecutor and presents evidence to the grand jury; the grand jury, in turn, decides if the evidence is sufficient to bring the case to trial.
Federal laws and court procedures differ from those of state courts. Although there has been a recent increase in federal drug cases, most federal laws involve complex issues or cases that involve activities in multiple states. Similar to state courts, federal courts require an attorney to be licensed to practice in the federal court or receive special permission to do so in order to appear in the court.
Like state criminal courts, federal criminal courts adhere to the "beyond a reasonable doubt" burden of proof for proving guilt. If a defendant is found not guilty, then he or she is released and the government is not able to appeal the verdict. The defendant may appeal a guilty verdict, while both parties can appeal the sentencing after a guilty verdict.