In the United States, both the federal government and the individual state governments have the authority to enact legislation making something a crime. Sometimes, a crime is solely within the jurisdiction of the state or federal government, while, in others, both the state and federal government could have jurisdiction over the crime. Both misdemeanors and felonies can be found among the many federal offenses. As a general rule, federal offenses are those that are committed on federal property or an Indian reservation, involve a high level government official or diplomat, or have an interstate commerce nexis.
State and federal courts within the United States operate essentially the same way; however, state courts are governed by state law, while the federal courts apply federal law. State courts may make laws that afford more protection to defendants than the Constitution guarantees, but not less protection. Many, but not all, federal offenses are found in Title 18 of the United States Code.
A crime, of any type, that is committed on federal property, such as a government building or a federal park, is within the jurisdiction of federal law enforcement and the federal courts. In addition, most crimes committed on Indian reservations are also considered federal offenses. Offenses that involve high ranking government officials or foreign diplomats my also be charged at the federal level.
The majority of crimes that are considered federal offenses, however, are considered within the jurisdiction of the federal courts because of their relationship to interstate commerce. Article One, Section 8, Clause 3 of the U.S. Constitution allows Congress to "regulate commerce with foreign nations, and among the several States, and with the Indian Tribes." The second part of the clause is often referred to as the "Interstate Commerce Clause" and has been used, and expanded, to form the basis for federal jurisdiction over a number of crimes.
Basically, the commerce clause allows any crime that may affect commerce, or that crosses state lines, to be within the purview of the federal courts. Common crimes that are considered federal offenses as a result of the interstate commerce nexis include kidnapping, bank robbery, and internet child pornography, as well as mail fraud and drug trafficking crimes. The interstate connection is easy to see in some federal offenses, while, in others, the courts have stretched the meaning of the commerce clause to include specific crimes. In a kidnapping where the victim is transported across state lines, the interstate connection is obvious. In other crimes, such as drug trafficking and firearms offenses, the theory is that the drugs or guns have crossed over a state line at some point during their lifetime and, therefore, can be considered to affect interstate commerce.