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Assistant District Attorney from WikiPedia:

In many jurisdictions in the United States, a district attorney (D.A.) is the appointed public official who represents the government in the prosecution of alleged offense criminals. The district attorney is the highest officeholder in the jurisdiction's legal department and supervises a staff of assistant district attorneys. Similar functions are carried out at the local level in other jurisdictions by officers named the Commonwealth's Attorney, State's Attorney, County Attorney, or County Prosecutor. Depending on the system in place in the particular state or county, district attorneys may be appointed by the chief executive of the region or elected by the people.

Because different levels of government in the U.S. operate independently of one another, there are many differences between persons who perform this function at the federal, state, and county levels.

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