Who is the district attorney for nassau county new york? MINEOLA, N.Y. (CBSNewYork/AP) — A career prosecutor has been sworn in as acting Nassau County district attorney. Madeline Singas replaces Kathleen Rice, who was being sworn in as a Long Island congresswoman on Tuesday. Singas, who is 48, was a prosecutor in Queens before joining the Nassau DA’s office in 2006.What is district attorney office? In the United States, a district attorney (DA) is the chief prosecutor for a local government area, typically a county. The exact name of the office varies by state.What is the district attorney? At the federal level, a district attorney is called a U.S. Attorney. Typically, a district attorney will have a team of associates - both assistant district attorneys and deputy district attorneys - that he or she supervises to manage tasks associated with cases.