Law enforcement in the United States

Law enforcement in the United States is one of three major components of the criminal justice system of the United States, along with courts and corrections. Although each component operates semi-independently, the three collectively form a chain leading from investigation of suspected criminal activity to administration of criminal punishment. Also, courts are vested with the power to make legal determinations regarding the conduct of the other two components.

Law enforcement operates primarily through governmental police agencies. The law-enforcement purposes of these agencies are the investigation of suspected criminal activity, referral of the results of investigations to the courts, and the temporary detention of suspected criminals pending judicial action. Law enforcement agencies, to varying degrees at different levels of government and in different agencies, are also commonly charged with the responsibilities of deterring criminal activity and preventing the successful commission of crimes in progress. Other duties may include the service and enforcement of warrants, writs, and other orders of the courts.

Law enforcement agencies are also involved in providing first response to emergencies and other threats to public safety; the protection of certain public facilities and infrastructure; the maintenance of public order; the protection of public officials; and the operation of some correctional facilities (usually at the local level).

Policing in the United States is conducted by "close to 18,000 federal, state, local and city departments". Every state has its own nomenclature for agencies, and their powers, responsibilities and funding vary from state to state.

At the federal level, there exist both federal police, who possess full federal authority as given to them under United States Code (U.S.C.), and federal law enforcement agencies, who are authorized to enforce various laws at the federal level. Both police and law enforcement agencies operate at the highest level and are endowed with police roles; each may maintain a small component of the other (for example, the FBI Police). The agencies have nationwide jurisdiction for enforcement of federal law. All federal agencies are limited by the U.S. Code to investigating only matters that are explicitly within the power of the federal government. However, federal investigative powers have become very broad in practice, especially since the passage of the USA PATRIOT Act.

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