Marrero (D) was a federal corrections officer. D carried a loaded .38 caliber automatic pistol, but he was not licensed to do so. D claimed that he was exempt from the law because of his status. By the terms of the law, it did apply to 'peace officers,” which was defined to include corrections officers. The statutory definition of peace officers includes correction officers of any state correctional facility or any penal correctional institution. The trial court dismissed the indictment. The appellate court reversed and reinstated the indictment. That court held that it only applied to state officers and not federal. At trial, D requested that the trial court instruct the jury on mistake of law because he reasonably believed that the exemption applied to him. The court rejected D’s argument that his personal misunderstanding of the statutory definition of a peace officer is enough to excuse him from criminal liability under New York's mistake of law statute (Penal Law § 15.20). The court refused to charge the jury on this issue and D was convicted of criminal possession of a weapon in the third degree. D appealed.