N.Y.C. Charter § 431: Section 431. Department; commissioner.

a. There shall be a police department the head of which shall be the police commissioner who shall be appointed by the mayor and shall, unless sooner removed, hold office for a term of five years.

b. Whenever in the judgment of the mayor or the governor the public interests shall so require, the commissioner may be removed from office by either, and shall be ineligible for reappointment thereto.

c. Whenever a vacancy shall occur in the office of police commissioner, a police commissioner shall be appointed by the mayor within ten days thereafter.