Md. Code, Courts and Judicial Proceedings § 5-402

(a) A merchant or an agent or employee of the merchant who detains or causes the arrest of any person shall not be held civilly liable for detention, slander, malicious prosecution, false imprisonment, or false arrest of the person detained or arrested, whether the detention or arrest takes place by the merchant or by his agent or employee, if in detaining or in causing the arrest of the person, the merchant or the agent or employee of the merchant had, at the time of the detention or arrest, probable cause to believe that the person committed the crime of “theft,” as prohibited by § 7-104 of the Criminal Law Article, of property of the merchant from the premises of the merchant.

(b) An owner or lessee of a motion picture theater or an agent or employee of the owner or lessee who detains or causes the arrest of any person may not be held civilly liable for detention, defamation, malicious prosecution, false imprisonment, or false arrest of the person detained or arrested, if in detaining or causing the arrest of the person, the owner, lessee, agent, or employee had, at the time of the detention or arrest, probable cause to believe that the person committed in the motion picture theater a violation of § 7-308(e) of the Criminal Law Article.