Complex sentence: Whether or not Mather was actually deputized has never been confirmed, but it is believed that he was because Las Vegas had a "no guns in town limits" ordinance in effect and Mather was armed.
Split into simpler sentences: Whether or not Mather was actually deputized has never been confirmed, but it is believed that he was. A "no guns in town limits" rule was in effect, a reason to believe that Mather was in fact deputized, as he was armed.