O'FALLON, Mo. (WLS) -- Police in O'Fallon, Missouri are investigating a series of armed robberies believe that the robbers used the Pokemon Go smartphone app to target victims, according to a post on the department's Facebook page. Four suspects were arrested early Sunday morning near the intersection of Highway K and Feise Road in O'Fallon after a report of an armed robbery. Police say they are suspected of multiple armed robberies in St. Louis and St. Charles counties in Missouri. A handgun was recovered.Police believe they used the game to, "add a beacon to a pokestop to lure more players" and then used the app to locate victims.Pokemon Go is an "augmented reality" game that allows users to capture, train and battle Pokemon who appear in the real world. Players can pick up supplies at real-world landmarks that serve as "pokestops" in the game.Pokemon GO users have also reported becoming injured while trying to catch the digital monsters.