A major problem for those analyzing U.S. criminal law and procedure is that it does not fit the Continental or British mold. There is no one single system, but parallel federal and 50 state systems each with its own legislature, laws, courts (including trial, appellate, and supreme courts), police, prosecutors and prisons. The authorities who enact and implement these laws are sovereign within their respective jurisdictions. Each state has police power over its people. The 10th amendment to the U.S. Constitution controls allocation of federal and state authority. It provides that whatever the Constitution has not designated as being within federal competence and jurisdiction or has not been denied to the states, belongs to each state, which has its own procedural system to enforce its criminal laws, within the framework of basic constitutional protections. The one unifying feature is constitutional law. U.S. criminal procedure is intricately and intimately intertwined with constitutional law. This has tremendous impact on law enforcement procedure and technique, including that on evidence taking, testing, and use in trial.
Primary responsibility of controlling criminality and defining crime rests with the states, although the list of federal crimes and federal jurisdiction keep expanding. Despite the fact that the individual states are generally in the forefront of the confrontation between the nation and the criminal, the dictates of the U.S. Constitution set the parameters of that confrontation. State constitutions may provide more protection, but not less. Today, many provide more. Thus, federal jurisdiction obtains for certain constitutionally listed offenses, including piracy, felonies on the high seas, crimes against the law of nations, and counterfeiting. The list of federal crimes and federal jurisdiction are expanding. Congress has promulgated several federal crimes, such as those relating to hijacking and terrorism. The federal government is assumed to have the authority to prescribe and enforce criminal laws relating to drug smuggling or tainting of foodstuffs because of the constitutional grant of power to protect national health and safety. Federal criminal law covers crimes involving U.S. government instrumentalities, such as post offices or national banks, foreign affairs, and crimes against instrumentalities established by treaty. Federal criminal jurisdiction also applies throughout federal enclaves--specially designated geographical areas such as military bases or national parks.
State and federal criminal law began with English Common Law, and statutory interpretation generally is based on basic common law concepts. Each state has evolved separately, however, with some selective inter-pollination. Each state has its own prescriptive, adjudicative and enforcement jurisdiction and its own procedural and enforcement mechanisms, limited by basic constitutional protections. Fragmentation of procedure and administration, thus, is a serious problem. In a large metropolitan area there may be more than one-hundred separate police systems, each operating independently of [and often competing against] each other. Tremendous variety exists in types and organization of police agencies, of prosecutorial agencies, of judiciaries; there are even two types of defense attorneys (public defenders and private lawyers). Looking from the outside, especially from nations where there is unity, supervision, and control, this may appear to be a pagaille de confusion.
46 Am. J. Comp. L. 605 (1998).
Blakesley, Christopher L., "La Preuve Pénale et des Tests Génétiques: United States Report" (1998). Scholarly Works. 331.