From the article: Police said that people in the crowd yelled threats at the couple and that the McCloskeys would not be charged. According to the NRA, state law does not prohibit the open carrying of firearms, but does prohibit exhibiting 'any weapon readily capable of lethal use' in an angry or threatening manner in the presence of one or more persons. Exhibiting a weapon in this way would likely be a Class D felony punishable by up to four years in prison and a fine not to exceed $5,000. According to the St. Louis American, however, the 'Castle Doctrine' allows people to use deadly force to attack an intruder on their property.