The task of the FBI is to investigate violations of the federal crime law and support the law. Protect the United States from investigating intelligence and terrorist activities from foreign countries, provide assistance to federal, state, local and international agencies in leadership and law enforcement, and perform their duties on the premise of responding to public needs and being loyal to the US Constitution. At home, it is only responsible for safeguarding national security and preventing organized terrorist activities; Externally, actively assist the U.S. Military Intelligence Agency (M.I.A, U.S. Department of Defense) and the Central Intelligence Agency (C.I.A, Central Intelligence Agency) in preventing and cracking down on all intelligence and military activities that may endanger U.S. national security. The official mission of the FBI is to uphold the law by investigating violations of the federal criminal law, protect the United States from threats from foreign spies and terrorists, provide leadership and law enforcement assistance to federal, state, local or international institutions, and perform the above duties according to public needs and compliance with the US Constitution. Every time the FBI investigates intelligence information, it will submit it to the appropriate American lawyers or officials of the US Department of Justice, who will decide whether to approve the prosecution or other actions. Among them, five aspects that affect society enjoy the highest priority: anti-atrocities, drugs/organized crime, foreign anti-espionage activities, violent crimes and white-collar crimes. The FBI once had a disgraceful history of supporting the law and sometimes even breaking it. But in the usual impression of most Americans, it is the most effective institution to fight crime. The number of agents is increasing every year, and now it has exceeded 1 1000 members. Most of the agents are stationed in foreign countries, working in the American embassy, and serving as the ambassador's legal commissioner. The FBI calls itself "LEGATS". The United States does not have a national unified police department like the China Public Security Bureau. The federal government has no unified police, only law enforcement agencies or police units distributed in various departments. Note that the United States has federal police, such as the National Park Service Police, which is different from federal law enforcement agencies. It's just that the federal police are small and unknown. In the United States, the police mainly refer to state police or local police below the state. Except Hawaii, which has no state police, other state governments have police departments, but with different names and different organizational powers. For example, California police only enforce the law on state highways and state government facilities, and its official name is California Highway Patrol. Comparatively speaking, the law enforcement scope of Texas Mounted Police is larger. In some states, in addition to the state police, there are specialized agencies similar to the US Federal Bureau of Investigation, such as the Tennessee Bureau of Investigation. Generally speaking, federal law enforcement agencies and state police only account for a small part of the law enforcement forces in the United States, and the real main law enforcement forces are county police and city police. The county is the largest administrative unit below the state level. One of the officials directly elected by the county government is called the sheriff. He is responsible for all the law enforcement tasks in the county, and usually has a police station in his office. Therefore, the official name of the county police in the United States in English is Sheriff' s counters, that is, deputy law enforcement officers. Areas with concentrated population in the county can be autonomous, and cities of all sizes in the United States are formed in this way. After the establishment of the municipal government, the administrative power was separated from its counties. The municipal government has its own police department. Unlike the county sheriff, the city police chief is usually appointed by the mayor or the city Council. The largest city police station is the New York State Police Department (NYPD), and the largest county police station is the Los Angeles County Sheriff's Office. Because local police don't interfere with each other, they belong to their own, so there is no unified symbol of police in the United States, and there is no unified title, and the weapons and equipment are different, although they are actually similar.
During the investigation of criminal cases, if the local police force is insufficient, they can ask the FBI and other federal law enforcement agencies for assistance. The FBI has certain advantages in some fields, such as crime analysis, criminal forensic medicine, etc., but it cannot exceed its authority to replace the police, and there is no so-called "FBI boss".