The assistant district attorney (ADA), or prosecutor, (or in Los Angeles Deputy District Attorney (D.D.A) and in Baltimore and Chicago Assistant State's Attorney (A.S.A.)) is the local public official who represents the government in the prosecution of alleged criminals. The prosecution is the legal party responsible for presenting the case against an individual suspected of breaking the law in a criminal trial.
ADAs from Manhattan, New York City work for the district attorney's (DA) office. They are supervised by an Executive assistant district attorney (EADA) or a Bureau Chief. In most Law & Order episodes, the ADA him- or herself appears on behalf of the DA's office during the initial arraignment of a defendant. Subsequently, the ADA is seen talking to witnesses as he or she helps the EADA build a case.