N.Y.C. Charter § 801: Section 801. Department; commissioner.

There shall be a department of investigation the head of which shall be the commissioner of investigation. The commissioner shall be a member of the bar of the state of New York in good standing and shall have had at least five years of law enforcement experience. The mayor may remove the commissioner upon filing in the office of the commissioner of citywide administrative services and serving upon the commissioner of investigation the reasons therefor and allowing such officer an opportunity of making a public explanation.