River City Casino in St. Louis, where a vigilant employee reported suspicious activity that helped launch the federal investigation into sex trafficker Mack Mitchell. According to a statement previously provided by River City Casino to Fox 2 St. Louis, one of its frontline employees noticed suspicious activity and alerted the property’s security team, which in turn contacted police. Mitchell arranged an Uber to collect the girl from Epworth Children’s Home before driving her from a St. Louis gas station to River City Casino. There, he introduced her to a woman who photographed the teenager and posted online advertisements offering commercial sex acts, prosecutors said. The girl engaged in commercial sex acts at the casino, with Mitchell receiving the proceeds, according to the plea agreement.