Police are investigating the armed robbery of a city cab driver that occurred on River St. The cab driver drove to the police station to report the incident. The cab driver advised police that he was dispatched to make a pick up at a residence on Vine St. When the cab driver arrived at the location, he reported picking up three black males. The destination for the passengers was River St. When the driver pulled up at a residence on River St., he noticed another black male waiting outside at the residence. The black male approached the cab and asked the driver for change. As the black male asked this question, the driver was robbed of $200. The males then ran from the scene towards Grove St.