Virtual experiments are used by the US Army to evaluate and obtain soldier feedback on new technologies. These evaluations are currently limited to obtaining soldier self-reports to determine the effectiveness of technologies and attain feedback for future improvements. Current virtual experiments are unable to accommodate external observers to spectate and evaluate soldier interactions with technologies due to difficulties in spectating the fast-paced multi-user interactions occurring during virtual experiments conducted by the US Army. In this paper, we present our research on identifying US Army requirements for a spectator interface and the design as well as development of a spectator interface system to address these challenges in virtual experimentation. A case study focusing on virtual experimentation for a human-robot teaming security scenario is then presented to demonstrate the usage and utility of the developed virtual spectator system.