Judge Hancock read § 15.20(2)(a) according to its ordinary language. In his view, the provision applies when a defendant acts under a mistaken belief that conduct is lawful and that belief is founded on the wording of a statute. Marrero's claimed belief—that the peace-officer definition covered Federal corrections officers—fit that language directly.
The majority, Hancock argued, improperly inserted a limitation that the New York Legislature omitted: the Model Penal Code allows reliance on a statute only when it is later found invalid or erroneous, but New York's statute contains no such phrase. Importing that restriction contradicts the text and makes the defense available only to someone who correctly relied on a law later invalidated, rather than to someone actually mistaken about a statute's meaning.
Hancock also maintained that the majority's interpretation defeats the Legislature's reform purpose. Section 15.20 was enacted to soften the rigid common-law rule that mistake of law never excuses liability, particularly where a person has acted in good faith under an official legal enactment. Limiting the defense to cases where a mistake negates specific intent would add nothing beyond preexisting doctrine and render the statutory reform largely superfluous.
On the asserted facts, Marrero's interpretation was sufficiently plausible to warrant a jury instruction. A trial judge had initially accepted it, and two Appellate Division judges agreed with it. Those circumstances supported Marrero's claim that he reasonably and in good faith believed the statute permitted his conduct.
Finally, Hancock rejected the majority's concern that recognizing the defense would unleash fabricated claims or overwhelm courts. Courts routinely distinguish genuine defenses from false ones, and the possibility of difficult factual determinations is not a reason to deny a defense that the Legislature chose to provide. Judge Kaye and Judge Alexander joined this dissent.