Prosecutors at different levels of government prosecute different types of crimes.
U.S. attorneys
At the federal level, prosecutors are known as U.S. attorneys. There is a U.S. attorney for each federal court district in the United States. The president appoints U.S. attorneys, who mainly serve as administrators. Assistant U.S. attorneys handle the bulk of the trial work. The U.S. attorney general, who is the chief law enforcement officer in the United States and the head of the Department of Justice, has supervisory responsibility over U.S. attorneys. The 94 U.S. attorneys and nearly 2,000 assistant federal prosecutors aggressively investigate violations of federal laws, such as white‐collar crime, drug trafficking, and public corruption.
District attorneys
On the state, county, and municipal levels of government, district attorneys (D.A.) are responsible for bringing offenders charged with crimes to justice and enforcing the criminal laws. In practice, district attorneys, who prosecute the bulk of criminal cases in the United States, answer to no one. The state attorney general is the highest law enforcement officer in state government and often has the power to review complaints about unethical and illegal conduct on the part of district attorneys. But only rarely does a state attorney general discipline a county or city D.A. for prosecutorial misconduct.
In rural areas, the highest law enforcement official is the county attorney. County attorneys working out of small offices prosecute criminal cases themselves. In urban areas, the highest law enforcement official is the city district attorney. The typical municipal D.A.'s office features a division of labor with special departments for felonies, misdemeanors, trials, and appeals.
Independent counsels
Independent counsels investigate high government officials, delving into accusations of everything from cocaine use by senior White House aides to perjury by the president. The purpose of an independent counsel is to guarantee public confidence in the impartiality of any criminal investigation into conduct of top officials in the executive branch of the federal government.
Some independent counsels have been harshly criticized for taking too long, spending too much, or criminalizing conduct other prosecutors would most often not bother with. Under the federal government's independent counsel law, the U.S. attorney general can appoint an independent counsel when the attorney general receives from a credible source specific allegations of wrongdoing by a high‐ranking government official. By 1999, the office of independent counsel had become so politicized and partisan that critics were calling for the repeal of the independent counsel law.