N.Y. County Law § 927
It shall be the duty of the district attorney of the respective counties of New York, Bronx, Kings, Queens and Richmond to prosecute all crimes and offenses cognizable by the courts of the county for which he shall have been elected or appointed, except when the place of trial of an indictment is changed from one county to another, it shall be the duty of the district attorney of the county where the indictment is found to conduct the trial of the indictment so removed, but said district attorney shall assist in the trial of an indictment removed to his county for trial, upon request of the district attorney of the county wherein the indictment was found. He shall perform the duties prescribed in section seven hundred of this chapter and such other duties as are prescribed by law.
N.Y. CountyLaw § 927