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In the United States, Special agent is usually the title for a detective or investigator for a state, county, municipal, federal or tribal government. An agent is generally an administrative worker for some but not all agencies.
Federal government 
Within the U.S. government, the title of 'special agent' is used to specifically describe any federal criminal investigator in the GS-1811 or Diplomatic Security Service FS-2501 job series as so titled according to the Office of Personnel Management (OPM) handbook. They are typically educated at least as far as the undergraduate level. Special Agents are typically armed and have the power to arrest and conduct investigations into the violation of federal laws. The title of "Agent," "Investigator," or "Background Investigator" refers to all other 1800 series job series designations to include:
– 1801 – General Inspection, Investigation, Enforcement, and Compliance Series; – 1802 – Compliance Inspecion and Support Series – 1805 – Investigative Analysis; and – 1810 – General Investigation Series
Although some federal agencies have recently entitled Background Investigators and other non-1811 personnel as "Special Agents," this is purely an administrative title and has no bearing on actual Special Agent Status. Some 1810-series investigators have the ability to conduct investigations and can be armed at times; however, they do not have arrest authority, which is what separates a traditional Special Agent (1811) from most other 1800 series personnel. Some 1800 series positions, such as Border Patrol or Customs and Border Patrol "Agents," do have the authority to enforce federal law, and thus have arrest authority; however, it is the 1811 Homeland Security Investigations Special Agents who have the authority to conduct major criminal investigations. Essentially, non-1811 personnel who do have arrest authority can be considered "Agents" while Criminal Investigators who carry a badge, gun, credentials, and have arrest authority are "Special Agents." All other 1800 personnel conducting investigations (background or otherwise) are "Investigators," "Background Investigators," or "Compliance Officers," no matter what their administrative title may be.
Federal agencies 
Most federal agencies have some type of special agent, investigator, or background investigator to include the following:
- Central Intelligence Agency (CIA) Office of Inspector General of the CIA
- Department of Agriculture (USDA)
- United States Forest Service Office of Law Enforcement and Investigations
- Office of Inspector General (USDA-OIG)
- Department of Commerce (USDOC)
- Department of Health and Human Services (HHS)
- Department of Education (ED)
- Office of Inspector General (ED-OIG)
- Department of Homeland Security (DHS)
- Coast Guard Investigative Service (CGIS)
- Immigration and Customs Enforcement / Homeland Security Investigations, (ICE/HSI)
- Customs and Border Protection (CBP)
- United States Secret Service (USSS)
- Transportation Security Administration (TSA)
- Federal Protective Service (FPS)
- Office of Inspector General (DHS-OIG)
- Department of the Interior (DOI)
- United States Department of Labor (DOL-OIG) – Office of Labor Racketeering and Fraud Investigations
- Department of Defense (DOD)
- Defense Intelligence Agency (DIA)
- Defense Security Service (DSS) – Non Law Enforcement
- United States Army Criminal Investigation Command (USACIDC)
- United States Army Counterintelligence (Army CI)
- Pentagon Force Protection Agency (PFPA)
- Naval Criminal Investigative Service (NCIS)
- United States Marine Corps Criminal Investigation Division (Marine CID Agent)
- Air Force Office of Special Investigations (AFOSI)
- Office of Inspector General (DOD-OIG)
- United States Office of Personnel Management
- Department of Justice (DOJ)
- Department of State
- Department of Transportation (DOT)
- Office of Inspector General for the Department of Transportation (DOT-OIG)
- Federal Motor Carrier Safety Administration (FMCSA)
- Federal Aviation Administration (FAA)
- Department of the Treasury
- Postal Service (USPS)
- United States Environmental Protection Agency (EPA)
- All 64 federal Offices of Inspector General (OIG)
Training for the federal criminal investigator 
Federal law enforcement training can be divided into various categories, the most common being basic, agency-specific basic (ASB), advanced/specialized, and agency-advanced/specialized. To operate safely and effectively, U.S. special agents and criminal investigators must possess skills and knowledge regarding criminal and civil law and procedure, enforcement operations, physical techniques, and technical equipment, to mention a few. They must also be physically fit. While possession of a college degree can aid in obtaining employment in this profession, only extensive training provided at specialized facilities, combined with on-the-job training, can provide the skills and knowledge needed to perform the duties of a federal criminal investigator.
U.S. special agents and federal criminal investigators generally receive their basic training at one of two primary locations: the Federal Law Enforcement Training Centers (FLETC), with facilities in Brunswick, (Glynco) GA, Artesia, NM, Charleston, SC, and Cheltenham MD or the FBI or DEA training facilities based at the FBI Academy in Quantico, Virginia.
Only DEA and FBI agents receive their basic training at Quantico. Because of politics, the FBI and DEA operate completely self-contained academies that provide all levels of training to their agents. These academies make no distinction between basic and agency-specific basic training. New FBI and DEA agents train at their academies for approximately five months before they begin their first investigative assignment. Both agencies' academies also provide advanced training in various subjects to other federal, state, and local law enforcement agencies. In fact, the FBI's National Academy is perhaps the most prominently recognized federal supplemental training resource for non-federal and non-U.S. law enforcement personnel throughout the world.
The FLETC, commonly pronounced "flet-see", is a consolidated training facility that provides basic and advanced training to U.S. special agents and other federal law enforcement personnel not employed by the DEA or U.S. Postal Inspector Service (USPIS). The FLETC also provides advanced and specialized training for most federal, state, local, and non-U.S. law enforcement agencies willing to share in the cost. The FLETC's basic training course for special agents, the Criminal Investigator Training Program (CITP) lasts about 13 weeks,and may be given to persons if required for self-protection depending on changes to program content or holidays. Nevertheless CITP only represents the beginning or basic training received by U.S. special agents not employed by the FBI, US Air Marshals, DEA, or USPIS.
After completing the FLETC CITP, most agents immediately transition to training provided by their own agencies (hence the term agency-specific basic, or ASB), lasting another 2 to 16 weeks and sometimes longer, depending on the agency. Some smaller agencies, like the 64 Offices of Inspector General (OIGs), operate consolidated academies, such as the Inspector General Criminal Investigator Academy (IGCIA), through which specialized but common ASB-type skills and knowledge are more economically taught. So agents employed by the OIGs first attend CITP, then attend the IGCIA's IG Investigator Training Program (IGITP), then attend their own agencies' ASB training after completing IGITP, receiving a total of up to 16 weeks or more of training before conducting their first investigation. Many of the agencies utilizing FLETC maintain their individual academies for providing ASB and agency-specific advanced training on the same grounds as FLETC and share use of the same facilities. Some agencies, such as the U.S. Department of State's Diplomatic Security Service and the U.S. Secret Service, conduct their ASB training in separate agency-owned and operated facilities.
Although a much smaller agency than the FBI or DEA, the U.S. Postal Inspection Service also operates a self-contained federal law enforcement training academy called the Career Development Division (CDD). Like FLETC and Quantico, USPIS CDD has been fully accredited by the Federal Law Enforcement Training Accreditation (FLETA). Like the other academies, CDD provides basic training to postal inspectors in firearms, legal use of force, driving training, crime scene management, controlled deliveries, felony arrests, case management, case development, informant management, and surveillance, but also incorporates agency-specific basic training to help prepare the USPIS candidates in enforcing postal laws and federal mail statutes such as mail fraud, mail theft, and other mail related crimes. In additional to basic training, CDD also provides advanced training for the postal inspectors, the uniformed postal police personnel, and the analysts.
For all U.S. special agents, training does not stop after basic and ASB. The career of a federal special agent is one of regular training in new legal issues and investigative techniques, and frequently includes quarterly, if not monthly, refresher training in hand-to-hand defensive tactics, the use of weapons of less than lethal force, and regular qualification in the use of firearms.
Criminal investigators and the use of the term special agent 
Not all federal criminal investigators are called special agents. Some federal agencies entitle their investigators as criminal investigators but use the term interchangeably with special agent. Other federal agencies use different titles for the same 1811 criminal investigative job series. Series 1811 criminal investigators for the U.S. marshals are entitled deputy marshals. Series 1811 criminal investigators for the U.S Postal Inspection Service are called postal inspectors. These inspectors were originally called surveyors and received a title change in 1801 to special agent. In 1880, the U.S. Congress created the position of Chief Postal Inspector and renamed these special agents to postal inspectors. The first Special Agents in the United States were appointed in 1791 when the Secretary of the Treasury was authorized to employ "Special Agents" for the purpose of examining the accounts and books of the Collectors of Customs. The position of Special Treasury Agent was created, and until 1860 submitted reports to the Department of Treasury, through the Collectors of Customs in the Customs District in which they were employed.
Other titles 
The titles special agent and secret agent are not synonymous. The title special agent is commonly the official title assigned to individuals employed in that capacity, especially by the U.S. agencies described above (and for the reasons described below), whereas secret agent is less of an official title, but is used to describe individuals employed or engaged in espionage. Special agents, like state, county, and municipal law enforcement officers, can, at various times, engage in secret or undercover activities as part of investigative operations, or counter-espionage assignments, during which they might be referred to as undercover agents. They may also be referred to, or refer to themselves, as criminal investigators, federal agents, U.S. Agents, U.S Special Agents, U.S. Federal Agents, agents, federal authorities, federal officers, federal investigators, or U.S. officers. The latter terms are merely descriptors and not formal titles. 1811 and 2501 series investigators are the only federal law enforcement officers allowed by law to conduct undercover investigations.
At the management level, the head of a region or office might be called a Special Agent in Charge, abbreviated as an SAC or SAIC. First line supervisors may be called simply supervisor or Assistant Special Agent in Charge, abbreviated as ASAC.
Jurisdictional issues 
Exactly which U.S. Special Agents have the broadest authority is a matter of debate. The issue of concurrent jurisdiction (in which two agencies have non-exclusive jurisdiction over a given set of the U.S. Code, such as the FBI, ICE, and DEA in respect to drug laws) does not make the issue clearer. However Special Agents of many agencies can often enforce Title 18 (general criminal code) of the US Code included in their agency specific duties. Some U.S. Special Agents have a larger number of Titles, or just different Titles, to enforce and with those titles sometimes include unique authorities.
The following are some examples of unique authorities that agency-specific Special Agents possess: Administrative subpoena powers. Department of Defense and any military Special Agents are authorized to enforce the UCMJ. Title 19 designation authorizes Customs officers to perform border searches, which require zero suspicion and no warrant.
Some agencies have designated lead agency by the Attorney General over particular types of investigations. The FBI usually is the lead in high-profile corruption cases of elected government officials. In another instance, the FBI is the lead agency among the member agencies within the Joint Terrorism Task Force.
There also exist many exclusive jurisdictions as well. In these cases, only one criminal-investigative agency is authorized or assigned jurisdiction over a particular Title or type of investigation.
ATF, DEA, FBI, USSS, DSS, USCG, CGIS, EPA Criminal Investigation Division, PFPA, USMS, and ICE/Homeland Security Investigations, special agents not only have the power to enforce the General Criminal Code (Title 18), but also applicable state and local laws, if so authorized by the state in which they are operating. DCIS, USACIDC, United States Army Counterintelligence, NCIS, and AFOSI special agents not only investigate statutes within the United States Code and state and local laws with a nexus to their branch; they are also tasked with enforcing the Uniform Code of Military Justice (UCMJ), a jurisdiction not held by most of the larger federal agencies. DCIS, USACIDC, Army Counterintelligence, NCIS, and AFOSI civilian agents enjoy statutory law enforcement authority. Other special agents, such as those employed by the National Park Service, have jurisdiction over crimes committed within the boundaries of or have a nexus to the lands managed by their agency or department only. Homeland Security Investigations Special Agents have administrative arrest powers under the Immigration and Nationality Act. They can administratively arrest and detain aliens for violations of United States Immigration laws pending federal removal (deportation) proceedings. HSI Special Agents can also seize merchandise and articles introduced into the United States contrary to U.S. laws under Title 19 United States Code.
Certain active-duty special agents employed by the military have broad authority, when the nexus of the violation they are investigating occurred on military-controlled areas or there is a military connection.
U.S. Railroads 
All of the major Class I railroads, most regional carriers, and some local railways employ their own police departments whose officers carry the title special agent. Railroad special agents are commissioned by the governor or other agency of the state they are employed in, are armed, and carry state arrest powers in all states in which their employing railroad owns property, if authorized by the state. Their primary concern is policing crimes against the railroad, although they sometimes have the authority to police the general public, make arrests on public property, and enforce applicable local, state, or federal laws when necessary.
State, county, municipal, and tribal governments 
A state or municipal criminal investigator may also be a special agent if so titled by the employing agency. This is the case in the Illinois Department of Revenue's Bureau of Criminal Investigation, the Georgia Bureau of Investigation, Ohio Attorney General's Office, Iowa Department of Public Safety, Virginia Department Of Alcoholic Beverage Control Bureau Of Law Enforcement,Tennessee Bureau of Investigation, and the Florida Department of Law Enforcement, for example.
Several Native American tribes also employ special agents as criminal investigators, court investigators, or gaming investigators and some are deputized as special federal officers of the Bureau of Indian Affairs.
See also 
- List of United States federal law enforcement agencies
- Law enforcement agency
- State bureau of investigation
- State police
- Drug Enforcement Administration
- DSS – Diplomatic Security Service, U.S. Department of State
- Federal Bureau of Investigation
- Society of Former Special Agents of the Federal Bureau of Investigation
- Police rank
- Investigator (disambiguation)
- U.S. Immigration and Customs Enforcement
- Bureau of Alcohol, Tobacco, Firearms and Explosives
- United States Marshals Service
- United States Secret Service