Cheyenne police are trying to find the masked man who used a gun to rob the Sinclair gas station at Little America at 10pm Thursday. Spokesman Sgt. Rob Dafoe says the robber is believed to be a white male in his 40's, possibly between 5'7 and 5'10 in height. Because the robber showed up exactly when the station closed and the station employee had the day's cash in hand, Dafoe says it's possible the robber had inside knowledge of the station's business practices. No one was injured in the incident, and Dafoe says the investigation is ongoing.