Just as there are levels of government ranging from local to federal, so there are criminal codes specific to each level of government. In other words, cities, states and the federal government each pass laws and ordinances consistent with their individual jurisdictions – jurisdictions roughly delineated by the Tenth Amendment to the U.S. Constitution. That amendment, part of the Bill of Rights, states as follows:
“The powers not delegated to the United States by the Constitution, nor prohibited by it to the states, are reserved to the states respectively, or to the people.”
So, the Constitution established a set of parameters outlining the responsibilities and authorities of the federal government. Everything else was left to the individual states and polities that comprise the United States of America. When discussing “public law,” then, it is necessary to draw this distinction. The laws of the United States are known as the United States Code, or U.S.C., or U.S. Code. There are 51 sections of the U.S. Code, each covering a different area of law within the purview of the federal government. Within those 51 sections, one in particular, Title 18, is specific to criminal statutes and procedures for enforcing those statutes. Title 18 of the U.S. Code includes such categories of criminal conduct as bribery of public officials, trafficking in protected animal species, counterfeiting of U.S. currency, and so on. The U.S. Code is, as noted, the compilation of all laws passed by the U.S. Congress, and represents the totality of those authorities determined over hundreds of years to fall under the purview of the U.S. Government. It is these laws that are enforced by federal agencies like the Federal Bureau of Investigation, the U.S. Secret Service, the U.S. Postal Service, the U.S. Fish and Wildlife Service, U.S. Immigration and Customs Enforcement, and many others. The U.S. Department of Justice is the principal federal agency responsible for enforcing federal statutes, but, with the exception of the FBI, the Bureau of Alcohol, Tobacco, Firearms and Explosives, and the Drug Enforcement Administration, all of which are part of the Department of Justice, most of the others are part of other federal agencies, including the Department of Homeland Security.
While the U.S. Code delineates the laws passed by Congress and enforced by federal agencies, city police departments, county sheriff’s offices, and state police departments all enforce laws specific to their individual jurisdictions. Unsurprisingly, there is overlap in jurisdictions, especially between city and county authorities, but each exists to enforce laws passed at different levels of government. City police enforce laws passed by the city governments for which they serve, county sheriff’s offices enforce laws outside of the legal borders of cities, and state police patrol highways and investigate violations of state statutes as opposed to city ordinances.