An act of shoplifting as defined herein, is hereby declared to constitute a breach of peace and any owner of merchandise, his agent or employee, or any law-enforcement officer who has reasonable ground to believe that a person has committed shoplifting, may detain such person in a reasonable manner and for a reasonable length of time not to exceed thirty minutes, for the purpose of investigating whether or not such person has committed or attempted to commit shoplifting. Such reasonable detention shall not constitute an arrest nor shall it render the owner of merchandise, his agent or employee, liable to the person detained.