<P> There are 93 U.S. Attorney offices located throughout the United States, Puerto Rico, the U.S. Virgin Islands, Guam, and the Northern Mariana Islands . As of June 2017, most of the U.S. Attorney positions have been held by acting or interim appointees since at least March . One U.S. Attorney is assigned to each of the judicial districts, with the exception of Guam and the Northern Mariana Islands where a single U.S. Attorney serves both districts . Each U.S. Attorney is the chief federal law enforcement officer within his or her particular jurisdiction, acting under the guidance of the United States Attorneys' Manual . They supervise district offices with as many as 350 Assistant U.S. Attorneys (AUSAs) and as many as 350 support personnel . </P> <P> An Assistant U.S. Attorney (AUSA), or federal prosecutor, is a public official who represents the federal government on behalf of the U.S. Attorney (USA) in criminal prosecutions, and in certain civil cases as either the plaintiff or the defendant . In carrying out their duties as prosecutors, AUSAs have the authority to investigate persons, issue subpoenas, file formal criminal charges, plea bargain with defendants, and grant immunity to witnesses and accused criminals . </P> <P> U.S. Attorneys and their offices are part of the Department of Justice . U.S. Attorneys receive oversight, supervision, and administrative support services through the Justice Department's Executive Office for United States Attorneys . Selected U.S. Attorneys participate in the Attorney General's Advisory Committee of United States Attorneys . </P> <P> The Office of the United States Attorney was created by the Judiciary Act of 1789, along with the office of Attorney General and the United States Marshals Service . The same act also specified the structure of the Supreme Court of the United States and established inferior courts making up the United States Federal Judiciary, including a district court system . Thus, the office of U.S. Attorney is older than the Department of Justice . The Judiciary Act of 1789 provided for the appointment in each judicial district of a "Person learned in the law to act as attorney for the United States...whose duty it shall be to prosecute in each district all delinquents for crimes and offenses cognizable under the authority of the United States, and all civil actions in which the United States shall be concerned ..." Prior to the existence of the Department of Justice, the U.S. Attorneys were independent of the Attorney General, and did not come under the AG's supervision and authority until 1870, with the creation of the Department of Justice . </P>

What is one role of the federal government's department of justice
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