Conn. Gen. Stat. § 53a-110: Affirmative defenses to criminal trespass.

It shall be an affirmative defense to prosecution for criminal trespass that: (1) The building involved in the offense was abandoned; or (2) the premises, at the time of the entry or remaining, were open to the public and the actor complied with all lawful conditions imposed on access to or remaining in the premises; or (3) the actor reasonably believed that the owner of the premises, or a person empowered to license access thereto, would have licensed him to enter or remain, or that he was licensed to do so.