An assistant district attorney (ADA) is a member of law enforcement who conducts criminal prosecutions on behalf of the city or county district attorney’s office.There are many different types of ADAs and positions depend on experience and specialty, such as civil or criminal law. Your primary duties as an assistant district attorney are to review all the evidence in a particular criminal case and decide whether or not to proceed with a criminal prosecution against the defendant. You interview police officers, witnesses, victims, and specialists about the case and consult with the district attorney before deciding to go forward, offer a plea, or drop the case.