Imagine a day when an unmanned aircraft can follow a homicide suspect driving on Interstate 880 and silently track him to his hideout in the East Bay.Police say that day is coming - possibly by next year. Remote-controlled aircraft known as drones will help their efforts to fight crime and make officers safer, and save taxpayers from the rising costs of fueling and maintaining helicopters.Critics, however, worry that law enforcement's use of the flying cameras will result in privacy abuses and open the door to the unwarranted surveillance of residents and, eventually, entire neighborhoods.