Unmanned drones are roaming American skies conducting surveillance on people in the United States, albeit in a "very minimal way," the head of the FBI revealed to Congress on Wednesday. Federal Bureau of Investigation director Robert Mueller said his agency's use of a small number of aerial drones is relatively new, and that the bureau has only begun to draw up policy and operational guidelines for the devices. "I will tell you that our footprint is very small," Mueller testified before the Senate Judiciary Committee.